You bring up a good point with "OCD is a real disorder and not just some bad habit". If a person's brain is truly exaggerating some common function, it's not like you have an immediate social support framework that is accepting and helps you deal with it, for starters.

I think the problem with this "you can choose your reactions" concept is that it is easy to apply it or receive it as a negative judgment. People have the reactions they do because they don't KNOW there is a way to choose in the first place.

Even though some people find altering their thought patterns helps as much or more than medications, it isn't ludicrously easy to simply drop a way of thinking or a specific behavior. The mind just doesn't work that way. It is doable, but it feels hard. It can feel as awkward as learning to switch your dominant hand, and that is after all as much habit as preference! Imagine trying to change your handedness ... for a while you wouldn't be able to write properly or even feed yourself well.

Habits (including thoughts, behaviors, emotional reactions) are challenging to break, because the "choice" is one you already made a very long time ago, when you simply did not know any other way of dealing with things. Very few people have trained psychologists for parents or teachers, let alone early friends! Even if they did, what if their technique doesn't quite mesh with your personality?