Them don't. .. insanity is doing the same thing again and again and expecting different result. I have talked to them but people believe what they want to believe
" insanity is doing the same thing again and again and expecting [a] different result[s]."
From a famous auote by Einstein.
" I have talked to them but people believe what they want to believe".
People have entrenched views - views that are difficult to change.
I have talked to them, together with preceding quote, suggests the speaker has talked to them over and over again, and now realises that it will always have the same result - they will continue to believe what they originally beleived, and they would not change their minds no matter how often the speaker tried to talk them out of their belief.
The "Them don't..." at the beginning suggests this is an informal - a colloquial - report, and that the speaker has changed his mind about how s/he is going to go about telling the audience about the situation.
"They do not ..." Perhaps s/he was going to go on to say "...change their minds no matter how often I talk to them", and changed their mind, mid-sentence.
As a supplementary aside:
It is very common to have entrenched views: this blogpost (link) discusses the ways in which people's minds are predisposed not to change, and some workrounds and approaches that have a degree of success in changing people's minds.
"I have talked to them but people believe what they want to believe" - I have already tried to explain or present my point of view to them, but they won't listen. People will believe things they want to believe, even if they are presented with good arguments to support an opposite view.
"insanity is doing the same thing again and again and expecting different result." - I have given up trying to explain my point to them. Repeating an action over and over again, and expecting it to result in something different is madness. Therefore, I won't repeat my action of trying to explain, because it hasn't worked so far, probably won't work in the future, and saves me from "madness"
This sounds like somebody saying that they no longer care about "them" understanding or believing him.