Can't Do 不能
Is 不能 only used when something is forbidden? I read that it means you can't do something, but not because of a lack of ability. For example, 我們不能說漢語。 would mean we're not allowed to speak Chinese, not that we don't know how to. But, can we use 不能 in any other way, like feeling morally obligated to not do something.
A: Just cheat!
B: No, I can't do that.