I would say that any persuasion technique that requires plain lies is unethical. Lies are contagious and break trust, while trust is required for any constructive communication.
Now, it may be a lesser evil in some situations. But a lesser evil is still evil, and should be avoided every time it can be. So yes, to me, you can call a technique itself unethical. Some exceptional situations may force you to do something unethical, because the alternatives are much worse, but that can be said to anything (you can always construct an hypothetical situation in which a given ethical rule will have to be broken), so if we want to keep that "ethical" word, we can apply it to something like openly lying.