It is absolutely a moral dilemma. It is immoral to defend something that you don't believe to be true.
It doesn't make any sense that arguing for something that isn't true will purify anything. This is the opposite of purity. Purity means you figure out what the Truth is, and then you defend that. Arguing for anything else just muddies the water for you and for everyone else.
I don't know what you mean by "negation of our self". Our self has nothing to do with it, what matters is the absolute Truth.
The real issue is that when we argue for falsehood, we are negating the truth.