How come former catholics now protestant will say catholicism isn't Christianity?

If you look in the book of Revelation, it talks about the seven lampstands who represent God's churches. The Roman Catholic church claims to be the one true church, when God acknowledges seven -- none of which match the description of the Roman Catholic church. Of course, one description does and that is the mother of harlots. If we know what the Bible teaches then it is not hard at all to figure out that the Roman Catholic church's doctrines do not line up. Some people are God's sheep and will read the Bible and recognize the truth. Some people are not God's sheep, the don't care about the truth and neither do they seek it. God's people stand for truth even if it's unpopular. The gate is narrow and few who enter.