Why is it that when debating, when we are wrong, and we get emotional, we lie?

That's Human beings for you.

People who do it..? Probably do it because they're SO invested in a certain viewpoint, they can't bear NOT winning that debate! And their need to be right, and convince the other person, overrides their need for truth... Which, in some cases? Might not have been very big, to begin with.

I don't think all people do it, however. At least not deliberately... I know personally..? I never deliberately lie to people, in order to win! (Although sometimes, I might be sincerely mistaken about something.) I'm a much bigger fan of admitting to uncertainties, and shades of grey, and the fact that there are plenty of things I cannot prove to people! So with spirituality and such, for instance, where that is very much the case..? I don't expect them to agree with me! Because I KNOW I cannot give them the sort of physical, scientifically reproducible evidence most of them require! But then again, that's pretty easy to do, for me... Because I don't believe they'll be forever lost, if they don't come to agree with me! Which is exactly what many Christians and other religious people believe... So I guess they probably feel like the end justifies the means, or some such.

Because after a person says something, even if it is wrong, they have a tendency to defend it.

Ask the Christians. They are the experts

Human nature.

However, intelligent, educated people don't enter into debates without being well-armed with information.

When you have strong beliefs that you want to be true it's not easy to deal with the fact that people can find flaws in your logic.

Who are you calling 'we'? I need no lies to debate any subject. We learned that lies never win debates. Facts win debates, not emotions or lies.

That is one reason christians always lose such debates, their belief is based on pure emotion, at the expense of facts.