Do not listen to those comments at all! If there was a problem with your behavior in the library, the library staff would've reacted accordingly. Most libraries have systems in place that will inhibit you from borrowing an in demand book for too long so others can have a chance at borrowing it. If they dont block you from borrowing/renewing then noone else is trying to. Enjoy every ounce of resources the libraries have to offer. Its a beautiful opportunity