Did Jesus or Paul ever attack someone who held a different faith?
No! Not just "NO", emphatically "NO".
Jesus cut loose on hypocrites of his own faith, Judaism. He never says, "Oh you apostate Samaritans, you're going to Heck." Or, "You Romans are messed up." No. And neither did Paul.
In fact, Paul lived 3 years in Ephesus, where the goddess Diana was revered. After 3 years, Paul had converted thousands, and the silversmiths were losing a fortune. So they whip up a posse to go kill him and his companions, and take him to city hall. The town clerk, realizing he has a riot on his hands, calms the crowd by reminding him they are neither "robbers of Churches, nor yet blasphemers", and if they have evidence or witnesses, they need to bring them forward. No one steps up, and the crowd is dismissed. (See Acts 19:21-41)
Think about it: After 3 years, no one among a rioting crowd could step forward to accuse Paul of preaching AGAINST Diana. NONE. Even though the silversmiths claimed to each other that Paul taught idols were not gods, which would have been blasphemy and treason if had Paul done so (Acts 19:26), the mayor notes it is not the case, and there are no witnesses.
Last time I checked the anti-Mormon sites, they were reminding everyone that Mormons are not Christians. We have a different Jesus. We worship a false god.
WWJD? What would Paul do? Well, we know what they wouldn't do.
So I guess we have another way, besides personal revelation, to know which preachers are corrupt. We can just watch and know that no missionary makes attacking another faith the focus of their ministry.
See Acts 5:42, 17:3; 1 Cor 1:17, 23; 2 Cor 4:5; Eph. 3:8; Phil 1:18; Col 1:27-28; 1 Pet 3:15.
Or I guess we could just ignore the Great Commission, and instead of teaching people to observe the things Christ taught, we could teach against every other faith.
Call us silly, but we Mormons are going to go with the Biblical model of preaching.