I think we should also examine what makes a bad hero, or what kind of heroic types really don't fit the romantic mould.
Politicians. I love politics, but it's not my life. By his or her nature, a politician must live, breathe and eat politics. That doesn't leave much room for the love interest. In romance, the love interest must take over their lives because their love is so damn important everything else is cast in shade.
Sports Jocks. For the same reasons as politics. There are a few sporting types who can put a few words together, but most of them are meatheads who devote their whole lives to sports. Once again. Girlfriends and wives take a back seat.
Drug users. Even reformed ones. Again for the reason that the love interest will always come second best. A person can have sworn off the booze because they once did a stupid thing and they've since reformed. That's OK, but anything more than that turns the novel into a drugs issue, rather than romance novel.
Cruel people. Dovetails neatly into Heidi's comment about not kicking puppies. Seriously, people who hurt animals are sick.