Well. Muslims profess to worship the God of Saint Abraham, and the God of Mother Mary, Who is the True God. So it is a little more complicated than that. If they formally reject Christ, then yes, they worship a false god. If they are in inculpable ignorance, and are worshipping God as best they can in the situation (e.g. if they live in a place where there are as yet no Christian Missionaries, or very few), then it is a different situation, as even the Pope Saint Pius X's Catechism admits. All the docuмent says is that Muslims profess to worship One God, the God of Abraham.
God is always True. Can the God of the Muslims who says hurt the infidels be the same God as Jesus, who said love your enemies do good to those who persecute you? That cannot be the same God. And isn't that how we know the new Jєωιѕн religion is not the same either because they ostracize non Jews?
This is why many of us know without a doubt that this post Vatican 2 stuff is not the same as the pre Vatican 2 stuff. (Sorry not a theologian, so some one needs to make it sound better.

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And I have to add Father Feeney to this list, because he also promoted hate towards people who didn't get it yet. There is absolutely no salvation outside the Catholic church, but that is God's to decide, not man's. We are obligated to teach the Truth, we are not obligated to force people to follow it. We are not obligated to make rash judgments.