Goblins are evil and my chaotic good Tav agrees with Wyll - let's kill the entire camp for all the reasons you mention.
*But* you accepted someone's surrender in exchange for information. Going back on that agreement is, at least, unlawful and -- I'd argue -- it's an evil act. He surrendered and he's helpless - Wyll should hold in his anger.
He also tortures an innocent human unless you stop him. Again, not a good thing and frankly too evil to count as an evil act. I mean the god of torture in Realms is evil And, as Niara has pointed out to me on a number of occasions, he's willing to abandon the "Save the Grove" quest when a good lead on his patron comes along.
I like Wyll - like SH he could end up evil or good. My guess is that once he finds Mizorra he'll face a choice and emerge as either neutral evil or chaotic good.
