Why are some unable express themselves appropriately when they disagree with others peoples opinions on topics?

my biggest frustration with debate is that one when person brings up an issue, people then deflect...to another issue. Its like everyone had ADHD.
example....lets say I bring up that I cant vote for Hillary because she is dishonest. If your response is that Trump is dishonest, my thoughts are this - "that may very well be true, I didn't say he was honest, I thought we were talking about Hillary. So, are we talking about Hillary, Trump, all politicians...what are we talking about"?

Good read. I'd guess it's likely comfort zones, pride, insecurities, and/or the hunger for power. Ignorance truly is bliss.