Even Tariq started an angelic plague to kill a villian, murdering an entire innocent town in the process. I have no doubt he would be encouraging Taylor to be a hero, I just don't think the PRT would agree with his definition of one. He was also perfectly willing to kill Kat despite her giving extremely generous terms for peace, because he was threatened by her sheer existence as a villian.
Yes, Tariq doesn't hesitate to do horrible things, but he does so only after trying everything else. There wasn't another way to stop Black from escaping and causing hundreds of thousands of innocent deaths.
And he's pragmatic and smart enough to not do so where the PRT can see Taylor. Or at all, given that the risk of discovery is very high. Tariq isn't a moron.
He wasn't offended by Cat's existence as a Villain, he was perfectly willing to ally with Cat at the Third Liesse. He was concerned that being a Villain and a ruler, she would make Callow's Story a Villainous one. Given that the other Villainous nations of Calernia are Praes, Stygia, the Everdark, Bellerophon, the Chain of Hunger and Keter, he's right to be afraid.