The FAQ on bip110.org says it's not about stopping spam, it's about making Bitcoin unwelcome to spammers. Should we try to do that? I think so. Does 110 do that? I think obviously yes.

The counter argument I hear a lot is something like "that's what fees are for" but as you point out, the mempool is completely empty. If that weren't the case I think changing the op_return policy would be less controversial.

Fees will price out spam someday but until then let's allow 100kb of arbitrary data per tx is madness.

Your second point is a valid concern but this is why core should not have forced an unpopular, unwanted change through on behalf of one company. When node operators objected they said fuck you, so here we are.