Are you looking for arguments against Signal?

I think the biggest one everyone will find and is very difficult to overcome is "My friends aren't there".

Other arguments like "it's centralized", "It's in the US", "It doesn't have feature X", "The client app doesn't have fancy stickers" are workable, have explanations or are a matter of time.

Thos saying "It needs to support SMS", are americans that weren't really using signal, but a glorified text app.

It's irrelevant to this community which is pro signal.

Signal provides a user experience comparable to iMessage in terms of features and ease of use, but with the big plus of cross platform compatibility.
That may not be what you personally are after, but it's what 99.99% of potential Signal users are after.

Signal tieing into the social graph we already have on our phones as user identifiers is a big win for 99.99% of users.
Signal being run through a centralised location is a big win for the 99.99% of users who don't want to host their own servers, or find someone to do it for them.
Signal attempting to earn income through things like money transfer is a good thing for the 99.99% of users who don't want to have themselves monetized in a different way (such as through showing users ads).

If a nation state wants to spy on you, you better be important enough to a different nation state that they protect you.
Because choosing to send GPG encrypted messages over XMPP isn't going to help you.