Good luck with the idea Vergil deserves justice visited on his ass. Might as well say Sparda deserved it too, after serving Mundus for so long in "the war" between the human world and the demon world, and only later deciding to help humans out. How many countless humans did Sparda see enslaved or killed, before turning on his own kind and killing countless numbers of them too? And who would even visit this 'justice' on beings that are basically like demi gods at this point? You might as well say Zeus should have had his ass kicked. Who's going to "punish" the sons of Sparda?
In any case, Vergil is apathetic to the case of humans for the most part, but since Visions of V is canon he's not entirely so - he does attempt to help humans escape from the Qliphoth in the city and saves a boy and his mother from roaming packs of demons because he sees himself in them. Vergil doesn't even consider himself human, so that's an act of charity for starters, even though most of the humans just consider him a freak for having the power in the first place to help them. With that kind of treatment, it's no wonder he doesn't care. Humans are more than happy to kill demons and a demon is what he considers himself to be. Asking him to give a damn about humans as a whole when he's an almost entirely pragmatic and logical creature seeking immediate self-preservation and empowerment is futile. This is a guy who knows Mundus' minions are going to come for him someday, thanks to their grudge against Sparda, as well as most likely guessing the demon hordes/Mundus intend to rule the human world again (which is the case of course in DMC1). Even if he doesn't gain enough power to defeat Mundus himself, it still makes more than enough sense that he must gain more power, because one way or another the demons and Mundus are an ever-present threat to both himself and the human world.
Even if you argue Vergil shouldn't have raised the tower, or that Dante ended up being just as powerful without having done the same things, that's leaving aside the fact Vergil was the one who truly awakened Dante's powers, not to mention his motivation to fight. Dante got powerful in no small part thanks to Vergil's actions. Dante, if he were ever going to truly try to protect the human world from the ultimate threat, couldn't do it without the demonic power gained from the previous action of freeing and incorporating the Sparda sword... which could only have been reached by Vergil's deliberate actions.
Besides, the sons of Sparda are not human, it's shown time and again they have very little in common with humans, and humanity is fortunate even one of them cares enough to bother about them at all. In the end, both cared enough to chop down the tree and stay in the Underworld. It's a human-centric view to assume these two owe their allegiance to humanity when it's clear most humans treat them with contempt. Enzo using Dante, Lady trying to kill Dante and badmouthing him for almost the entire game of 3, the humans in the city looking down on V for helping them, even the Fortuna order were just using demons and Sparda for their own nefarious purposes... if anything Dante fights demons not for humans but just to satisfy his own sense of righteousness/revenge.
From a risk/benefit analysis perspective, the collateral damage from Vergil's actions was worth it because as a result both he and Dante ended up being uber-powerful protectors toward humanity and not enslavers.
The demon world is still there and is still full of potential Munduses desiring to rule both the Underworld and the human world someday. Better they exist in their powerful forms now than if they never had, because without them the humans do not stand a snowball's chance.
