IMO the main issue with locking Minthara behind a stupid evil decision to massacre a bunch of innocents for dubious personal gain is that *she* is very much not that character. Minthara is definitely still evil after you recruit her, but she's extremely practical *lawful* evil, and she even calls you out on slaughtering the tieflings, implying that in your position (absent a compelling reason) she wouldn't have done the same. If we got someone like Korgan for killing the tieflings, it would make a lot more sense, because the companion you get lines up with choice you made, but there's a clear disjunct there with Minthara - and gating her behind THIS choice seems arbitrary when there are many ways she could survive your encounter and still end up in her 'starting position' in Act 2.
Slight digression: A lot of people are talking about the lack of content for an evil playthrough, and I actually think it's less a lack of content and more a failure to properly gate content behind actually evil choices, such that it's only readily available to evil characters. For instance, it's easy to see an evil-aligned character infliltrating the cult for answers/potentially seeking to take control of it, and working with the cult for that purpose. The problem is that all of this content is easily available to a good character - everyone assumes you're a genuine True Soul at the outset, so you get the run of the goblin camp and moonrise towers without even trying, and no-one actually requires you to do anything particularly evil until the end of each respective Act. IMO, both of these areas should have been gated behind some pretty morally dubious actions (and/or actually difficult skill checks) such that this content is significantly curtailed unless you're willing to get your hands dirty. At minimum, Moonrise should not be fully open to you if you side with the Harpers against the Drider at the start of the act, PARTICULARLY as you find out later that the Chosen are aware that there is a rogue true soul running around with the Astral Prism.
It's also a bit jarring that none of the Absolute's minions seem to communicate...like, at all. You can slaughter every true soul you come across in Act 1, kill the Drider in Act 2, and generally make it clear to anyone with functioning eyes that you are *not a friend* to the cult, but no one ever really seems to call you on it until you openly declare war on them. These are high level characters with access to powerful scrying magic, and even failing that, it's unlikely that you've slaughtered your way through the absolute's forces without leaving any survivors to report back. The cult should at least be aware of the major highlights of your previous actions, but they just...aren't.
