I like to point out in such circumstances that they have undoubtedly lied some time in their lifetime. Does that mean I should immediately disbelieve anything they say, up to 'The sun is shining' because, according to CT logic, once a liar always a liar.
I personally believe repeating a lie because you believe it yourself is forgivable, but requires repentance and compensation to those damaged by the lie. What is not forgivable is lying when you know that you are. If you knowingly lie, you ARE a liar.
I think it is a safe assumption that if you lie about one thing, given the motivation you will lie about anything.
I have a weighty disadvantage when dealing with folks like yourself and that is that I am constrained by my own morals and ethics to only make claims that I believe myself to be true. I may be wrong and I do not deny I have been before, but if you prove it to me I will admit it. I don't see where you've proved anything in opposition to my claims, you've simply waved hands ,piled on ,declared me a loon and claimed I am unqualified to have an opinion or reach a conclusion.
I believe that if I lie to you even though you identify as my enemy that I have dishonored only myself. I may not reveal weaknesses, but I won't lie about them.
Your position seems to be that it is fair game to lie to me and about me because I am the opposition, you have a far different set of rules to abide in that gives you a tremendous advantage. You do realize that, don't you?