Is Gerald a bad person?

Whether or not you consider Gerald Croft to be a bad person is largely a matter of opinion. However, there can be little doubt that he's not the most likable of men. He comes across as being a spoiled, entitled, privileged aristocrat who thinks he can do whatever he pleases in life. Unlike Sheila or Eric Birling, he has no sense of any social responsibility towards the lower orders. If anything, he only seems to think of protecting his elevated position in society, whatever the consequences. Gerald did once arrange for Daisy to stay at a friend's flat, but that was only because he felt pity for her. And in any case he proceeded to take advantage of Daisy, making her his mistress.
Not only is Gerald incapable of any moral growth, he doesn't want to grow, anyway. It's notable that he, more than any other character in the play, is determined to unmask the inspector as a fake. Whereas the inspector acts as a catalyst for the development of social conscience in Sheila and Eric, he causes Gerald to become defensive. If the inspector turns out to be an impostor, then Gerald will be off the hook. Right up until the end, then, Gerald is thinking of protecting his good name instead of facing up to the truth of what he's done and atoning for his guilt. Whether or not this makes him a bad person, at the very least it indicates great selfishness on his part.