I do not agree with you describing Fischer as crazy, I'll do my best to explain it. Someone is called crazy, when he can no longer control his thoughts or actions.
Simply because Fischer attacked the Americans politics doesn't mean he's crazy, maybe he has different political opinion than yours and you just have to accept it. Well if anyone who doesn't like the american politics and the Israelis is called crazy, then more than 60% of the population will be crazy, since Russia, China, pretty much all Africa, the Arabic world and many other countries don't agree with the Americans.
Is Julian Assange or Edward Snowden or others crazy?
Even Bin Laden wasn't crazy. A murderer? No doubt about it. A hater? of course. A man with no conscience? True. But he wasn't crazy because he calculated his every move, he had goals, he knew his enemies, and he knew what he was doing.
Someone who calculates his moves is probably not crazy, might be evil because he uses his intelligence for the wrong purposes, but not crazy.
I'm not gonna discuss the right and the wrong, everyone judges it from his own perspective, i think there's no right and no wrong in politics, politics is always dirty, the dirtiest hands usually wins. Ask the CIA, or any intelligence agency around the world, all are ready to do the bad actions for what they think is the greater good.
So what is crazy? John Nash was definitely crazy, at some point in his life, a schizophrenic who won Nobel prize in economics. See John lost it, he couldn't control his thoughts, Fischer was just against the american politics there's nothing wrong with that.
Let me ask you a question, is Kasparov crazy? He's against the Russian politics and been arrested for that reason, just like Fischer. so if you want to call Fischer crazy, you should do the same with Kasparov.
To answer the initial question, there's no doubt that someone who's intelligent might be crazy, he overthink stuff and might become a conspiracy theorist. What you define as crazy is normal for him, or other people who think the same way, what's normal for the spider is chaos for the fly.
Al Mutanabbi once said
ذو العقل يشقى فى النعيم بعقله . . وأخو الجهالة فى الشقاوة ينعم
That with intellect suffers in bliss with his mind
And the ignorant in misery lives blissfully
So what he's trying to say is simple, ignorance is a bliss.