Certainly mental gymnastics are part of RPing. Nobody ever said any different. But there are limits. There's a point where it's no longer mental gymnastics and you're simply excusing bad writing.
For example: I'm considering having my blueside MM go vigilante. So, when she's running the Clockwork arcs, she's thinking "sure, I'll help out $CONTACT in eliminating the Clockwork. And make notes and pocket a few choice bits while I'm at it". My character, my reasons. My story.
But when you're forced to introduce elements like "I'm being mind controlled" (to take an example introduced above) in order to play through an arc... That's not mental gymnastics. You're mentally covering up for bad writing taking away your control of your story. It's OK to choose, it's bad to be forced.
"Forced" above is italicized, bolded, and underlined for a reason - it's the key concept in this discussion. One that folks don't seem to grasp. Nobody is asking for the world to suit my character. We're asking for choice. (Choices can be fettered or limited, no problems there - so long as the choices exist.) We're asking to retain agency and control of our own story. That's what makes an RPG different from a VN or choose-your-own-adventure.