It's not wasting time. We understand that the Catholics who post here in all probability are not going to change. We are told.however to stand against error and to rebuke sin and error "before all". Not doing so would be disobedience. Those who read these threads need to see the truth from scripture. Of course it should all be about Jesus but that is not what Catholisicism is.
But hope springs eternal in the human breast.
We also know that many folks who may be neither Catholic, Protestant or even Christian who may read these threads and gain more info from them than they'd get by attending Catholic, Protestant or even atheistic services.