And in doing so, such Protestants are saying No, Catholic, you do not believe what you say you believe. Quite the opposite! You believe what WE say, and you're quite evil and decidedly naughty for doing so.
THAT is bearing false witness.
This is the great divide. You are telling Protestants they are "naughty" for not accepting the authority of the Church and all its teachings, at the risk of hellfire. And yes, we are saying you are "naughty" for bowing to idols and praying to other than the Trinity.
There's a reason there's this schism. Only one of us is right, since both cannot be right. Either we are right, or Catholics are right. And only the Lord can judge the "naughtiness" of the side that's wrong. I, personally, will not risk the wrath of the Lord (I'm a big enough sinner without adding to it) by kneeling before images of Mary or saints, and directing prayers to them as if they can hear or intercede. I'm sorry, but I am convinced that's idolatry and I won't risk that one.
We live by grace, but as Paul said, does that mean we should sin so that grace may abound? God forbid!