saved tens of thousands people.

Tens, if not hundreds of thousands of people have died in Tariq's lifetime due to his actions in support/denial of wars/crusades. If he didn't back the 10th Crusade, how successful would the initial mustering of Heroes and troops really have been? Would it have even happened? How many people died simply because of that one action? How many thousands more would have died if the Crusade was successful?

Sure, Black's actions were leading to the deaths of innocents, but Tariq isn't blameless in getting Black there in the first place.

the Heroes’ attitude would be perfectly reasonable.

In Calernia, because the masses are brainwashed to think that anything the Heroes do is gold, even if it's really shit. That doesn't make many of their actions reasonable or even acceptable.

99% of the past Villains really were insane backstabbing mass-murderers

The majority of Heroes we've encountered are insane, with a good number being backstabbing, and a number being murderers. Is combining them really the only thing that makes someone a Villain?

And even now, except for SoS, MK and BoM, the Heroes look quite reasonable.

Most of the Heroes only work with/for Cat because Nessy is on the field and Tariq & Hanno say to, not because they actually believe that she has a point. Even Tariq only works with Cat out of necessity rather than belief. That's not what I consider 'reasonable', just not suicidal.