I think such rpgs are not designed for evil gameplay, because being simply evil does not make sense in 99% of cases anyway.
You would need a completely different plot designed for interesting evil gameplay, especially when it's not only "killing good guys" but interesting interacting, plotting and intrigues. Almost every game trying to enable a designated good and evil walkthrough would fail. Good to some sort of greyish is the best someone could expect (I'm okay with that), but interesting evil walkthrough which does not break the actual campaign is very hard to implement.
The only good way to do it now would be to make it run parallel to the good path and that seems to have been the intent Larian had by introducing Minthara, however she can betray you and then you end up with nothing at all. If she was guaranteed to be a recurring character it would be a little better, but Act 1's evil path also seems to be a closed narrative with failsafes (such as the goblins being out of the picture in a "by the way, the entire camp is aggro now lol bye" way).