It should say "<Sender> is simping", with an optional "for <target>". ie, "/simp" would just say "deanveloper is simping", but "/simp mikveloper" would say "deanveloper is simping for mikveloper".
I feel like the whole marriage command is a good example of "if you don't like it, don't use it". Similarly to RPs, the only outside effects of marriages would be "marriage advertisements" which shouldn't be nearly as bad as RP advertisements.
"Mocking marriage" is just a kinda lame argument...