making a character likeable and an asshole is amazingly easy. therell always be someone out there ready to woobify the most despicable of villains - even pennywise got a thirsty little fanclub. somehow. (there are like, sociopolitical reasons as to why some villains get woobified and some dont, mainly racism, but point still stands that flat out villains can charm the socks off people, let alone antiheroes)
the thing is, like, nobody's 100% bad? people do horrible, irredeemable things, but not every thought, intention, and action they have is dripping with malice. and if you create a 3-dimensional character, no matter how reprehensible their actions, this complicated humanity shines through, and people will love them (not everyone, but hey ho.) an example of a really likeable but Bad protagonist is moist von lipwig in terry pratchett's going postal, making money, and raising steam. hes a conman, and a self-confessed slimy geezer, but he's very carefully humanised both through keeping the perspective close to first person, so you see his internal world, through his relationships, and through small, inconsequential mentions of his history (a mention of being a runaway, or a memory of his mother, which are very off-hand and light, but add sudden depth to the character.)
or hell, fagin from oliver twist, thats an interesting one! what a rotten geezer, but also a father figure, and a carer (albeit a crappy one.) when theres subtlety and variation to a characters decisions that provide depth and humanity, something to love can be found.
personally, a big thing in my comic is grey morality. the two main characters are on either sides of a war, and both have been raised to believe that their side is right, and persecuted, but theyre not 100% sure. the MC is based on a villain in the original myth, so she does a lot of bad things, some by choice and some not, and has to find ways to live with that. there were originally some fairly 2D no good villains, but as i started developing the story they all turned into something closer to tragic heroes (except one guy, whos just a twat - ya gotta have one). the story got instantly more interesting when the characters behaviour and motives had that depth to them, and it gives me more places to lay down the theme 'you have good reasons for doing what you did, but it was still wrong, and you have to live with that.'