No idea if this kind of discussion is allowed on the wiki.
I was playing the other day and didn't have the Goblin Tinkerer yet. I noticed that the guide says, "Are goblins really so different from us that we couldn't live together peacefully?"
This implies that the goblins are intelligent (though violent) and have clashed with the humans in the past. Indeed, they are the only non-human (not counting skeletons because they are presumably undead humans - or even goblins!) race in Terraria that have specific "roles", e.g. Peons, Warriors, Archers, etc.
The goblins also have the only non-human NPC (minus the truffle (I have no idea why he exists except for maybe the dryad, though that's for another day.) ). The goblins also both consist of the male and female genders, according to the Summoner's wiki page. The humans are the only other species where this is true.
The goblins also wear non-decaying clothing (hey, it has to be said) and are capable of using bows and magic, which, again, is something only humans or undead enemies do. Harpoons can be dropped by goblins even after the Tinkerer is saved, showing that some other goblins must be able to create them.
Now to much more speculative stuff.
The goblins only attack once a player's HP has been increased by an amount and they, presumably, have various NPCs. Perhaps the reason goblins did not attack the player until the because they did not pose as much of a threat? It would make as they do not actively seek to kill other NPC's in the world like the Angler.
This would also explain why Goblin Summoners also only appear in Hard Mode - the player is now skilled enough to warrant the stronger opposition.
The goblins may even be justified in attacking the player. If Goblin Scouts are killed and enough Tattered Cloth is collected to craft a Goblin Battle Standard, a goblin army can be artificially summoned. And are they really to blame? After all, you have killed 15 of their own.
So to recap, goblins are the dominant species of Terraria alongside the humans.
What do others think?
I play mobile, so I only know about 1.2 stuff. Is there anything from 1.3 that I missed?