Increased commerce? Not if everything is produced by Acme corp because no one sees any value in uniqueness. Reduced conflict? That's pitiful. If people hate each other, it's not going to matter if they speak the same language or not. It's probably better that they don't.
Yes, there are pockets of America that maintain an identity of their own, but they're few and far between. Cultures get assimilated and eradicated. It takes decades, but eventually they fade away. I live in an area that had a strong french presence, but now, decades later, there's no sign of it. I miss the cuisine and conversation. It won't be back. I don't think the community is better for it. It certainly hasn't turned the town into a more bustling economic presence and it hasn't lowered the crime rate. We just lost something interesting and became just like the towns that border us. Anywhere, USA. Population us.