If they are in opposition to Catholic Doctrine, they are wrong

Augustine:Why Argue Against Non-Catholic Beliefs?

Because, if they are in opposition to Catholic Doctrine, they are wrong.

Why Not Just Argue for Catholicism?

There's nothing wrong with this method. In fact, I think it is the one most recommended in Scripture:

1 Peter 3:15
King James Version (KJV)
15 But sanctify the Lord God in your hearts: and be ready always to give an answer to every man that asketh you a reason of the hope that is in you with meekness and fear:

But rebuking and correcting are also advised:
2 Timothy 4:2
Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all long suffering and doctrine.

If you prefer, think about it in terms of a standardized test: you use the process of elimination to eliminate the wrong answers. What remains is the right answer.

In my opinion, its not always that clear cut. For instance. Salvation by faith alone.

The fact is that many Catholic Church Fathers have correctly preached salvation by faith alone. HOWEVER, they have also preached, in the very same breath, salvation by faith and works.

In our zeal to defend the doctrine of faith and works from the Protestant complete rejection of works as a basis for salvation, Catholics have taken the opposite and equally false position of denying the Doctrine of salvation by faith alone.

However, the Church Fathers who used this term, faith alone, did not mean what Luther taught. They meant two things:
1. We are saved by our expression of faith in Christ, in the Sacraments.
2. We are saved by submitting to the Faith of Christ in the New Testament as opposed to the Mosaic Law of works in the New.

Does anyone hear a word coming out of my mouth? Do you understand why I say that this is not clear cut? The fact is that I frequently, 99% of the time, argue against salvation by faith alone, because I know that the person arguing in favor of it, does not realize that there is a Catholic understanding of the term. I don't think that even most Catholics realize this. But that is what St. Paul was teaching when he said:
Titus 3:5
King James Version (KJV)
5 Not by works of righteousness which we have done, but according to his mercy he saved us, by the washing of regeneration, and renewing of the Holy Ghost;

And the Church Fathers when they said things like this:

Ambrose (339–97): Therefore let no one boast of his works, because no one can be justified by his works; but he who is just receives it as a gift, because he is justified by the washing of regeneration. It is faith, therefore, which delivers us by the blood of Christ, because blessed is he whose sins are forgiven, and to whom pardon is granted.

Jerome (347-420)

Romans 10:3: God justifies by faith alone.

He who with all his spirit has placed his faith in Christ, even if he die in sin, shall by his faith live forever.

Ambrosiaster (c. 366-384):

God has decreed that a person who believes in Christ can be saved without works. By faith alone he receives the forgiveness of sins.

Romans 3:24: They are justified freely because they have not done anything nor given anything in return, but by faith alone they have been made holy by the gift of God.

Romans 3:27: Paul tells those who live under the law that they have no reason to boast basing themselves on the law and claiming to be of the race of Abraham, seeing that no one is justified before God except by faith.

This is because Catholicism admits both/and logic. Christ is God and man. The Church is human and Divine. We are saved by faith apart from works in the Sacraments. And by faith and works in the final Judgment.

So, its not always clear cut. But I do advise, whenever possible, show them their error.
1 Corinthians 11:19
For there must be also heresies among you, that they which are approved may be made manifest among you.

Sincerely,

De Maria