What’s wrong with making friends with goblins?
The DMG says (p. 260) that you get XP “[w]hen adventurers defeat one or more monsters-typically by killing, routing or capturing them ...”
That means there are atypical ways of defeating monsters - turning them into friends is one of these.
Naturally, there should be risk, sacrifice and challenge in the social encounter just as there would be in a combat encounter and as DM you are free to adjust the XP award as you see fit. Remember that players respond to incentives: if war-war pays better than jaw-jaw then that’s what you’ll get and vice versa.
Oh, and friendships in D&D always create complications.
A recent session saw us come face to face with a blue dragon. This is in a sandbox campaign so we had no way of knowing if this was a fight we could win. So we humiliated ourselves, flattered and bribed the dragon and lived to fight another day.