I think it's fair to say that the majority of table top role playing games operate under the assumption that the player characters are the good guys. But now that I've typed that out, what does it even mean to be the good guy? To start with, it doesn't necessary mean that the PCs are paragons of virtue free from moral ambiguity. In some games, like Cyberpunk Red, the PCs are most often criminals but are they the bad guys? Well, no, I wouldn't say so. The PCs are usually going against violent gangs and mega corporations that toy with millions of lives in an effort to raise the price of their stock a few points. In my experience, PCs are more likely to protect a food co-op in the inner city from corporate interest seeking to kick them out so they can turn the building into a condo. For the purposes of this thread, I'm going to define good as leaving things better than you found it without harming innocent people. This may be a bit simplistic, by philosophers are still debating what is good and we're probably not going to come to a satisfactory answer in a thread on En World.
How many roleplaying games out there exist where the PCs are the bad guys by default?
Vampire the Masqurade is the best example I can think of. In Vampire, the PCs are, well, vampires, who literally have to prey on other humans to survive (though a PC could theoretically live on animal instead of human blood). Especially in 5th edition, it's only a matter of time before a vampire hurts or kills a human being and this includes those the PCs love. The PCs are monsters.
An early release version of Blade Runner is available for those who backed the Kickstarter. Based off the 1982 movie of the same name and the recent 2017 sequel, characters are blade runners, police officers tasked with hunting down rogue replicants and retiring (killing) them. These replicants are nearly indistinguishable from human beings making Roy Batty and company runaway slaves. In Blade Runner, player characters make their living tracking down and killing runaway slaves. You might argue that Roy Batty was a dangerous murderer, but a slave rising up and killing his oppressors is perfectly natural in my book.
What other games are there were the PCs are bad guys by default? Feel free to disagree about whether the PCs in Blade Runner or Vampire are "bad guys" if you'd like. I can't control you guys and it'd be foolhardy to try!