but you will never force protestants to convert by telling them they are heretics.
I never called a single Protestant a heretic - very few of them are. Only a Baptised Catholic can be a heretic. They are, however, followers and members of a church which teaches heresy.
It is better to be charitable to our brothers and sisters in Christ and to love them and pray for them—that the Holy Spirit will guide them to the truth.
I am being charitable - I am telling them of the dangers of the path they are embarked on. If there was someone who denied the divinity of Jesus and said that all religions were bunkum, would you take such a “charitable” line?
I challenge that suggesting Protestantism is anything less than a heresy and a direct afront to the Catholic Church and Jesus Christ is charity; it is not. Charity springs from love and compassion and care - and I care enough about these people to tell them the truth.
Protestants do what they do because of ignorance, or a feel-good emotional rush. Or because they have been indoctrinated with hatred of the Catholic Church. Those are the only reasons - if someone was doing something which lead them into danger because of these reasons, charity would tell you to tell them of it.
With all due respect, I think your approach is counter-productive.
And I think that doing anything else is not only counter-productive, but is also not what Christ wants. Notice that Christ Himself and all the Apostles go around and offer a very black and white, hard-line teaching on what the Truth is. And most of them get killed for it!
You say that we should pray that the Holy Spirit shows them the truth; I say that Christ told us to teach all nations, not just to pray for all nations. Evangelisation is the Great Commission - and when there are heresies they have to be crushed. As a significant number of Bishops who are now Saints did.
Am I likely to be remembered as a Saint of the Church who crushed Protestantism? No. Am I likely to meet people in Heaven who I have converted to the truth of Catholicism by simply stating the bare facts? Yes.
Look at the arguments thrown from the other side - the idea that Catholicism is not Christianity and so forth. Look at what the Islamics say - that Christianity is a lie. That is zeal, that is determination. That is why they are winning converts - because they do not bimble around and say "Well, you get a pass . . . "
Nope, they say that those who they think are wrong are wrong - and people convert in the face of conviction and no truth whatsoever!
We have truth and practically no zeal - is it any wonder that the Evangelical cancer grows day by day?