I'm a big fan of Snyder's Superman, who is above all a good man despite what some haters erroneously posit, but I've got a few concerns in this direction as well. I'm not too worried that he'll kill innocent civilians while incoherent, though it's certainly not impossible.
The bigger issue is the nightmare timeline. I liked that Whedon basically removed it from the theatrical JL, as it was a subplot that I didn't really care for in the first place, and which requires a whole lot of attention in order to pull off - more time than I think we are actually likely to have in a "mere" four hours. That's a story which definitely revolves around a killer Superman.
Regardless of whether Evil Superman is the product of Anti-Life, and I think there's pretty ample evidence that he is, it still feeds into this broader cross-media narrative that [IF] Lois = dead → [THEN] Superman = Evil. There are some fans whose favorite thing about Snyder's Superman seems to be that he'll eventually evil, but to me it's his fundamental good nature. "The only way to disappear for good would be to stop helping people altogether, and I sense that's not an option for you." And his eventual proposed heel turn seems so much at odds with the way he's characterized the rest of the time that it legitimately annoys me.
I think it's
worth being dismissive of the idea of Superman turning evil because Lois dies. After all, nobody ever posits that Batman would turn evil if he didn't have Robin, although maybe somebody should, or that the Lone Ranger without Tonto would start running a gang himself, right? Or that Mary Jane is the only thing keeping Spider-Man from being a mad scientist just like Doc Ock or Vulture. Yet plenty of stories from Brave New Metropolis to Nevertheless She Persisted imply that Superman is an emotional weakling whose existence as a hero is contingent on Lois Lane, and I am bloody sick of it, because it doesn't even make sense in the stories that posit it. Only Ending Battle and the televised Crisis stand in opposition to this ideological
infestation, and frankly we need more stories like them.