For most of you, people with paranoid disorders are encountered more frequently online than in regular life. Not for me, of course, but my situation is unusual. I would like to explain them to you a bit. Parts of their thinking that seem strange are quite reasonable once you understand what they are starting from. They may end up in a crazy set of ideas, but the reasoning to get there often makes an internal sense. This is part of why you can't argue them out of these ideas. It's not that their reasoning is broken, it's that something else is broken. Chesterton's first chapter of Orthodoxy goes into the idea quite well from the perspective of a nonprofessional writing over a century ago. And fun.
First, they retain most of the knowledge and abilities they had before, not necessarily impaired in any way. If she knew horses well, she still knows about horses; if she played the cello well, she can still play well. She may have developed suspicions about people in the horse barn or the orchestra. These may grow until she can no longer manage to stay involved with either. She may or may not be attracted to new theories that explain things to her and decide that horses or music are far more important in the cosmic scheme of things than others have noticed.
There is a sense that some things are important that others have overlooked. In the same way that theme music plays in a movie, telling us that the villain has arrived, the person with paranoia has a sense (quieter, though no less sure) that something ominous is occurring when they hear the news or even just go to the supermarket. The number 7 is occurring too frequently, there are people who have Russian names, or look Russian, the cashier exchanges a look with the bagger that tells the person she knows something. They wonder for a time what it all must mean, but settle quickly on an explanation. The brain will not allow events to stand unexplained. They must be fit in somehow. The insignificant data that is regarded as significant continues to accumulate. This is supplemented by real data , sought or unsought. The ATM has twice not been available when you needed it most. A guy who you met just last week and told about these growing plots has a car accident. There must be a Russian (or more frequently, a Jew) behind this. Those forces are signalling to you to back off. They know you are onto them and will punish you.
Think what this must be like from the inside. This plot is real, you know it is. You try to explain it to others to warn them, but they cannot be made to see. The fools. They must be stupid, or unobservant, or easily misled, because what else could it be? These things are obvious, but no one believes you. You conclude that you must be very knowledgeable, very important. You see behind the superficialities and know what is really happening. That thing you call the news? It's just what they want you to think. If you were religious, that is likely incorporated in to give you a special status. Even people who were naturally quite humble will get caught up in such things. "I'm nobody important myself, but God has called me to preach this message." And what is the message? "That the last days are happening." "That I am a prophet." Or "That people should love more." There are other variants for Eastern traditions.
One would think that with such rigidity the specific delusions would remain constant, but this is not always so. I have had patients whose explanations have changed over the years, though they deny this. On a milder note, I know people who are sure that the non-obvious is more real than the obvious who have changed their focus for exactly who is pulling the strings over the years. (If it goes on long enough, it seems to inevitably become the Jews.) Memory changes as well. It is very common when bad events happen for many of them to say "I predicted all this long ago, but you wouldn't listen." There is an advantage online is that sometimes you can go back and check what they did say, and no, they didn't predict this. What happened is that they had a sense way back then that something was wrong and that evil would come of it, and they had many suspicions. They said something. When the bad event occurs they remember that one, or something that vaguely looks like it and insist "I told you so. I knew." As they have suspicions about everything, all the time, it is hardly surprising that they had suspicions in 2015 or 2012. They change their memory - I think almost instantly - of what they thought then.
Nonetheless, it becomes one more reinforcing bit of data. I have been saying brilliant things for years, but no one acknowledges me. It only goes to show how evil the great powers are and how stupid nearly all others are. It has all happened again.
It is hardly surprising that they are particularly upset at those who tell them that they are psychotic, and they devote energy to sloughing off that claim. They will tell you that the psychiatric medications recommended make you psychotic, which is 10% true - true in certain circumstances that are easily remedied. They will sometimes even focus on a particular mental health professional who they believe has ruined their life. I never had any of these problems in life until they brought me to the hospital and I had Dr. Katz. Yes, and you didn't have to wear a cast until they brought you to that other hospital and Dr. Killani put one on you, but that doesn't mean he broke your leg.
They are attracted to other paranoid theories and may come to adopt them as better explanations than their own, and they gravitate toward other paranoid people, but these seldom last. They cannot sustain relationships with people who don't agree, and sometimes this has to be 100% or nothing. Even the groups that have stability over time do not often have stability of membership. People drift out. There are Feeneyites who claim that they are "just traditional Catholics" that have existed as groups for decades. Yet (I am told) the individuals last less than a decade in the fold. They move and become regular Catholics with a bit of paranoia in the background, or they drift away altogether, or decide that they have been duped and aggressively make some other religious choice. The great multiplicity of hate groups the SPLC keeps uncovering is often the same guys leaving one small group and starting or joining another. Not that this is noted by the Dees group, who attract funds by identifying as many problems as possible.
Does this paranoia get better over time, receding on its own? I don't think so. My observation is that it grows worse: more strident, more disconnected from reality, more bizarre. I admit that is not a professional opinion or supported by any research I know of. It is my impression, both online and from live experience, but both could be unrepresentative samples.
Are they dangerous? Well, we are all dangerous. If they have lots of money or power they could become dangerous. If they are trained in weaponry or martial arts they could be. If they can exploit a particularly technology, sure, dangerousness could flow from that. Only a little different from the rest of us. I had a friend long ago who had paranoid schizophrenia, who believed the people next door to him were killing babies in the basement. That might prompt any of us to turn violent to try and stop that, mightn't it? Yet he was a gentle soul, and so just kept reporting it to the Nashua PD and picketing the front of the house with signs. He could not stomach being violent himself. Yet I have known other gentle, responsible souls who did become at least somewhat violent over time because they had just had it. They saw no other solution. I would say "more than the average person, but perhaps still not very much." Here is a story about the lack of predictability to scare you. Up in Wolfeboro about two decades ago there was a paranoid man who lived off on his own, deep into his property, who seldom came out over thirty years except to buy a few things. The police had known about him for years and even had a pretty good relationship with him. Someone wished to speak with the man - perhaps to buy property? I forget - and asked the police if it was okay to approach him. The PD assured him it was. The visitor drove up the long dirt driveway, got out of the care and waved, asking to approach, and was shot. You would think a track record of thirty non-shooting years would be enough to make a prediction from.
On the internet, you have no way of knowing whether this is a guy who is making serious plans or just a guy in an attic grousing.