Perspective on Roman Catholics (Particularly Baptism)

Please pardon the incomplete nature of this post, relative to the topic. As usual, I am not intending to provide a thorough treatise on the matter. I composed these thoughts as part of an email exchange, so you are missing some context but hopefully this is helpful.

We (reformed,presbyterian,covenantal,etc) view baptism from the objective standpoint of "God's Word determines its meaning rather than our own understanding," therefore we should consider our responsibility toward Roman Catholicism in similar fashion as we do Credobaptists. Granting that the errors in each are significantly different, we must still maintain that the errors in both are significant. We should treat the Roman Catholic church as an erring brother in need of instruction, admonition, exhortation, rather than being a right arm trying to saw off a left leg.

Is it the official teaching of the Roman Catholic church that salvation is earned by works? Is it the official teaching that Mary is a Savior/Divinity in addition to or in place of Jesus? Are there one hundred and one other errors taught from the pulpits of Roman Catholic churches and Protestant churches every week?

This boils down to the great issue of 'the objectivity of the Covenant.' If a Southern Baptist pastor divorces his wife to marry his girlfriend and is known to blatantly lie and steal from the church treasury, but doesn't come under the discipline of the church, is he still a Christian? Those who say that Roman Baptism is not baptism will surely say that the man is not a Christian. Those who say that Roman Baptism is baptism will surely say that the man is a Christian. As was recently and rightly pointed out by a brother in Christ, the objectivity issue stems from "who decides what means what?" If God defines baptism, we don't have the authority to decide if a Trinitarian and Christian church's baptism is valid or not. If God has given objective parameters through which we are initiated into and/or expelled from the Covenant, then we cannot add subjective viewpoints as to who is in or out.