The only thing that makes an evil “lesser” is that there is less energy going towards supporting it. By putting it into power you make it the greater evil. “Lesser evil” shit is something everyone has to unlearn if they are ever going to help anyone. How far capitalists and the state are willing to go is as far as they think they can get away with. If any capitalist or politician is being held back by morals, they will be replaced by ones that aren’t. If there is a profit margin to squeeze, anyone willing to squeeze it gains that power. People can get away with a lot more with less scrutiny, so the lesser you think their evil is, the more of it they can get away with.
The “lesser” fascist is still a fascist, and fascists spend much more of their time attacking us than attacking each other, and on top of that even if they do attack each other it’s through attacking us.
You haven’t explained how that is supposed to work though. Why couldn’t the greater evil do this, what’s stopping them? And you truly think that every political party has the very same goals underneath? Let’s take an extreme example: Germany 1932. You think if the SPD (social democrats) had won the election instead of the NSDAP, it would have been just as bad? You think they would have also slaughtered all the Jews and started WW2, because they were secretly just as evil? That doesn’t sound reasonable or realistic to me. There’s more to politics than whether a party is capitalist or socialist. Nuances exist.