Being a realist has nothing to do with not being able to tell jokes. That is stupid. They are just being uptight. Oh wait, am I being a realist?

I can say with certain I am one of these boring assholes called 'realists'. There certainly are people who tend to just be jerks who want to shoot down people for their own self confidence. However, there are many people who just hate ignorance. For example, if someone comes up to me in the labs i teach (physics labs) or on a forum and tells me that they think the speed of light is not constant, I try to put them in their place. The ironic thing is that THEY are the ones trying to force their beliefs on other (and what you said, "accept a lot of things", is exactly you forcing your beliefs on others). The appalling part is that these people, who have done 0 work to show they're right, are spitting in the faces of tens of thousands of physicists and millions of manhours of work and billions of dollars worth of carefully crafted experiments that show such a statement is false. Plus it contributes to societies that simply reject scientific thought. They're the societies that spend billions of dollars on hocus pocus cancer cures and pills that claim to magically help you lose 50 pounds by eating nothing but chocolate. And yes, in the US, the billions of dollars figure is accurate.
And that example is something rather trivial for the average person! What about gambling? Many people feel there are systems to beat "the house". "The house" is not stupid. Mathematically they always win. Las Vegas wasn't built by winners. Infact, casinos know they can trick people by letting people occasionally win big due to the statistics of it all and end up with bigger profits. Try to tell this to the average gambler and they'll scoff at you and listen to the guy who said he has a lucky method where they kiss the screen because one time a thousand years ago they hit a $50 jackpot on a penny slot by doing that.
It wouldn't be so bad if these kinda people end up leeching off society. When their fortunes go south, they go on unemployment or commit crimes which effect everyone. It also contributes to this mindset of everyones opinion is equal and all ideas should be held up as worthy. The thing is, you know you agree to what I'm saying. Why? Would you fly on an airplane if I, with 0 piloting experience, declared that I know how to fly the airplane? Of course not because you know my opinion needs to be supported by some facts or information or else it is meaningless.