I got a 6 months male who has been used to freely wander outside. 

I'm wondering about letting him go outside. I live at the second floor and share a balcony with my neighbor (a entrance balcony, which means that the cat could go out if someone opens the entry door). That seems dangerous for him.

I wanna point out that he's very happy cat, always playing, cuddling with me, etc. But he's also quite fierce and rash.

The thing is, he often meows at the door like he's genuinely hurt and I can't stand it, I want it to stop. I'm thinking about just letting him go, even if I live in a big city. Could that be that bad of an idea? Or could there be another way to distract him from going outside? Could castration help?