URSF stands for User Rejected Soft Fork. If miners were to activate BIP110, URSF nodes would reject this so the chain splits between BIP110 nodes that enforce the new soft fork rules and URSF nodes that don't. It's a way for users and miners to say: we're not going along with your soft fork, and we'll keep using the Bitcoin protocol as it was.

The spam supporters don't like the idea of Bitcoin being clean of spam and not abused by large jpegs and other arbitrary large data. So they attack BIP 110 to reject clean Bitcoin blocks from BIP 110 which will lead to chain split. They will create a spamcoin similar to bcash. They do it becuase they profit from spam on Bitcoin.