What can we say?
The Evil Path Needs Some WorkI fail to see how attacking the goblins during the tiefling fight could be rationalized by evil characters, even goblin characters, but moving things around a little does open the possibility of us not immediately falling in with the Tieflings
First of all being evil doesn't need to mean being interested in joining the bad guys, much like not being given an option to join Sarevok or Irenicus isn't a shortcoming for those games. But in BG:3 we are given a thin 'in' into the cult, siding with Minthara doesn't even directly lead to it, you have to side with her, then suborn her into your scheme. The problem there is that, I have very little idea what our motivations for going through all of that is, are we on board with the Absolute or is it just a long con to get us into a position to remove the tadpole. Either option might be interesting but it's also not very supported by the game, of course my experience siding with Minthara is very minimal so people should chime in with how that route has developed.
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As for moving things around to make siding with the goblins more natural:
Instead of having our first encounter with the mercenaries be a cutscene of them hammering on the gate followed by unavoidable combat, move it back so that we run into them still trying to get to the grove, how this encounter goes down could be very depended on how you're roleplaying your character and their alignment
Aradin: quick! we have to make it to the hidden grove goblins are on our tail!(sic)
*G: Of course lets go/fight/hide
LG: Whatever happens we can't lead them to your grove, we'll fight them here -->persuade?
NE: Good luck with that...(Odd, goblins don't usually tussle with druid groves)
LE: You'd be willing to draw those things to your people, turn around and face them or I'll kill you myself ->intimidate?
CE: Things look pretty bad for you guys, I think I'll just put you out of your misery now.
Now you've got a scenario where you might be the ones who kill the mercenaries followed by an encounter with the goblins who were chasing them...in fact in this scenario finding the grove actually becomes you're main objective similar to how killing the goblin leaders is your main objective now...it could work.
I've also just realized a bit of a plothole, the goblins are chasing Aradin, but as soon as they find the grove they should be either sending someone back to tell the war party, or just turning back all together.