I'd call it borrowing, not renting. In my experience, renting implies that you paid money to use something for a short while. Borrowing implies that you did not pay money and were gifted the use of something for a short while.

That being said, I definitely prefer to buy. I annotate my books and I can't do that if it doesn't belong to me. But I am always looking for deals and ways to save money on books. And I appreciate that libraries are there for people to use and to make reading more accessible. But I'm also in a place where I can personally afford to buy my own books and I'm grateful for that fact.

I don't really much care if someone else borrows or buys their books. They're still a "real" reader in my eyes either way.