The question of Appropriateness

[Fang]

Actually, most OCD behaviour or 'mental illness' does not let the person with OCD chose if it wants to OCD or not. Once started the OCD acts as its own compartmentalized identity overriding your 'own' will no matter how much you sob, scream or sulk.

You're right, people don't get to choose their mental illnesses lol, however you've missed the point.
There is a difference between behaviour specific to an illness and behaviour in general by a person with that illness. Someone with OCD is going to be triggered by certain scenarios to act in a certain way in accordance with the predisposition provided by the condition but that is only in situations relevant to the triggering of the condition, not for all the decisions the individual makes.

You still get to make your own decisions, everyone has their limits as to what decisions you are capable of making but you still get the opportunity no less.