I was on a stipend during grad school. And I was grateful, rather than resentful, towards the undergraduates and taxpayers (in my case, far more of the latter than the former) who paid for it.
I enjoy exploring ideas that are emotionally unpleasant, but which it's hard to construct a logical argument against. Some unpleasant ideas turn out to be correct!
It's fine to be grateful, but a grad school stipend is not charity. You are being paid to perform a service. If the undergraduates (or more commonly, their parents) and taxpayers did not think research and teaching were useful, they wouldn't pay you.
I enjoy exploring ideas that are emotionally unpleasant, but which it's hard to construct a logical argument against. Some unpleasant ideas turn out to be correct!