They keep the discussion alive, which gives us an opportunity to present the truth for inquiring minds.
Seriously, though, the "Calvinist revival" connected with Banner of Truth and other organisations had forged a kind of united front against Arminianism. So there is a shared space in the Calvinist world where we recognise salvation issues are more important than baptism issues. The problem, though, is that infants are people too, and they must be saved. That is where I prefer to direct the conversation. If infants are saved it is because they are in the covenant. But in discussions of this kind they are often presumed to be excluded from the covenant, as if they are not saved along with the rest of God's people.