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What if the ideas are unethical?Then argue the case for that position and tease out the ethical ramifications with your interlocutor. Bring a lot of evidence to back up that argument. Argue against the strongest form of the opposing idea(s), don't just create straw men to knock down or attack simple weak spots for easy points.
Unless the person advancing an unethical idea is intentionally trolling, take them seriously and seek to engage & explain your point. But it also requires truly understanding the other side (hence why you should be able to both articulate and argue against the strongest form of their argument).
Humanity has had some pretty awful ideas over its brief history. We have a mixed record when it comes to eradicating them by dialogue vs fighting. Usually we try dialogue for as long as we can. Too often, we wind up fighting when dialogue fails. Changing hearts/minds isn't an easy task. But the more we vilify, insult, ostracize, and otherwise verbally (or physically) attack those whose ideas we deplore, the more they frequently dig in on their position because they've tied their own identities to their beliefs. It's a funny condition with people that they often hold their identity as a believer in thing X far more strongly than they actually hold thing X.
[edit: wording & a little extra explication]