Re-Animator is about a mad scientist. We know this instantly because the movie opens up with a zombie outbreak in a medical college, and after the violent scuffle dies down, one of the teachers turns to a student and blames him for the mess. The student, named Herbert West, is defiant: he didn't create a monster, he just give a corpse life and then soon afterwards that corpse tried to violently murder people. As Jeff Foxworthy could have said: if there's a big difference between those two things in your mind, then you just might be a mad scientist.
If we didn't grasp that Herbert West was mad at first, it wouldn't take us long to figure it out. After all, his re-animating solution is the sort of nuclear color that only appears on hazmat suits and in Mountain Dew bottles, so the audience immediately knows that they shouldn't want it in their bodies. West's way of speaking is also troubling - he doesn't tent hit fingers like Mister Burns does, but he always seems like he's on the verge of doing it. Also, he's a terrible roommate. Sure, he pays the rent on time, but then he does medical experiments on the cat when no one is looking.
As a person, West has two basic problems: one, he needs to tone it down. The cackling is a dead give away that he's the sort of person who might be a cat murderer. Two, people are creeped out by death, so all of his death-centered research would seem creepy even if it was legitimate. Yes, conquering death would be an important medical discovery, but has he thought about trying cure baldness or create boners? Sure, if he did go into those fields anti-pharmaceutical pundits would probably get in his face about how he's wasting society's resources on trivial problems, but he would become a guy you'd want to talk to at a party, instead of being the guy who makes you regret accepting the invitation.
Alas, it seems doubtful that West is going to take that advice. He's a mad scientist down to his bones, and that means that he doesn't care about normal concerns like baldness or bloodless boners. Sure, his chosen occupation has it's roadbumps - it's going to get him kicked out of multiple medical schools, and staying in a rented room on a regular basis is going to be kind of a challenge, and oh, yeah, there are the occasional violent outbursts from the newly undead to deal with. But that's all small potatoes for a guy like Herbert West. If you're going to make an omelet, you're going to have to break a few eggs, and if you're going to conquer death then you're going to have to create some undead things, and if those undead things want to break you like you were an egg, well, c'est la vie. In a way, that sort of dedication is admirable, even though it's obviously insane.
That said: I am not letting that guy anywhere near my cat.