You can already join Lae'zel in pressuring the tiefling into kneeling and grovelling. I imagine that you don't get to push him at least in part because they didn't want to bother animating it when you can get the same result with just words. The issue I've always had with alignment-based choices in games is that it's very rare that the choices can take into account your intentions with the choices. So say Tav says some racist things to ingratiate themselves with agroup of thugs, with the intent of turning on them and killing them when the opportunity arises, that shouldn't tick your evil meter up the way being genuinely racist would. And adding/removing options based on alignment can be a tricky thing to do in games, if the devs end up locking actions that logically should be available to any alignment. And I really don't trust Larian to interpret alignment very well, so I honestly think the game is better without it.
