Contending for the Faith Against False Teachers

I have regular apologetic and evangelistic interactions with pseudo-Christian cults, mainly Mormons, Jehovah's Witnesses, and Oneness Pentecostals. In each case, someone always says something like this: "Why do you judge us? Why can't you just go practice your beliefs, and leave us to practice ours?" It's a form of guilt manipulation, trying to make it seem as if I am just a big meanie.

Yet, their repeated "why's" have an answer: the commandment of Scripture.

First, we have the warning against false teachers: "Do not listen to the words of the prophets who prophesy to you, filling you with vain hopes. They speak visions of their own minds, not from the mouth of the Lord. They say continually to those who despise the word of the Lord, ‘It shall be well with you’; and to everyone who stubbornly follows his own heart, they say, ‘No disaster shall come upon you'" (Jeremiah 23:16-17). The danger of false teachers is that they leave their followers under the wrath of God, while blithely imagining their safety. That is why false teachers are so popular. "While people are saying, 'There is peace and security,' then sudden destruction will come upon them as labor pains come upon a pregnant woman, and they will not escape" (I Thessalonians 5:3). And it isn't just the cults which are the danger here. The popular TV preachers, such as Joel Osteen, are equally dangerous. They promise peace and prosperity, but never mention sin or the wrath of God. So their followers march, grinning and satisfied, into the waiting maw of Hell. 

In the face of such deceivers, the Scriptures give me a stark warning: "If I say to the wicked, ‘You shall surely die,’ and you give him no warning, nor speak to warn the wicked from his wicked way, in order to save his life, that wicked person shall die for his iniquity, but his blood I will require at your hand" (Ezekiel 3:18). If I see the false teacher and those deceived by him, and I make no effort to warn them of God's judgment, then God holds me guilty of their death! 

That's why the New Testament also gives every true Christian this commandment: "I found it necessary to write appealing to you to contend for the faith that was once for all delivered to the saints" (Jude 1:3). I do not face accounting to cultists or other false teachers for challenging their errors; I face the wrath of God if I fail to do so.