So I agree that the "evil" path still needs more work, but what you're describing here sounds more like Murder-hobo-ing, which is a very distinct, "me vs. the world" kind of evil.
At least last time I played, my problem with the "Evil Path" (or more accurately, the Cult path) is that it's not really tempting or aligned to your character goals enough enough - the cult does very little to sell you on joining their side. If you're not hostile to her, Minthara just starts ordering you around, basically going like "you gonna join or what?". At most she mentions that you'll be "first amongst her favorites" if you guys successfully destroy the Grove, whatever that means. Honestly, I might have forgotten, but I'm not even sure why the Cult wants the Grove gone, other than Cult = bad.
The Cult doesn't offer you any solutions in terms of removing the tadpole, nor do they make a convincing case that you should keep it in there (which I think might be the way to go). It always felt like such a jump for my character who's #1 goal is to remove the tadpole to suddenly join in with the tadpole cult, without getting a thorough convincing that the tadpole should be kept.
I think the problem is one of assuming that the rewards are the only reason to align with the goblins. There are RP and POV reasons to align with them as well. Let's consider it from the perspective of those who respect strength.
-The Goblins, Minthara, Dror Razglin etc...have an active army that has dominated the countryside and is searching for the Druid grove to destroy them.
-The Goblin Camp are all trained fighters unified and organized into Warbands. (There is some internal competition but its not an issue)
-The Goblins have accumulated a lot of treasure from the raids they have been carrying out. They have food, money, and magic.
-The Goblins have clear leadership (again with some internal competition, but they are all firmly on the same side and not trying to destroy each other)
-The Goblins have strong allies supplying them(Zhentarim).
-The Druids/tieflings are hiding from and are in fear of discovery.
-The Tieflings and Druids have some warriors and Druids. They are not organized nor are they unified. Most are untrained.
-The Druids and Tieflings are running out of food and supplies, the cupboards are bare. Druids have moved to Goodberries to sustain.
-The Druids and Tieflings are on the verge of civil war. Shadow druids are making a play for control. ArchDruid is being held prisoner by Goblins.
-The Druids have no strong allies. They have some animals and Volo. No one is supplying them. They are trapped.
For a character that respects strength the choice is clear who you should side with here. Its VERY hard to respect those in the Druid grove - as those unable to protect themselves are basically useless; after all isn't that the definition of innocent? What use are the Druids and Tieflings as allies? None. Best to wipe them out and plunder what resources they have to strengthen yourself before they end up in the hands of an enemy.
