I liked Grant in Agents of SHIELD and then they made me utterly despise him.
I hated Donna Noble and then she became one of the best of the Doctor's companions.
Turning in a negative direction is dangerous, though. After Grant irredeemably turned I almost stopped watching. And anytime he showed up from that point on it damaged my interest in whatever was going on. It's odd that I can like to hate a character, but not if it was a character I once liked.