These people do not decide. They have seen the effects first-hand.
Perhaps seeing it from the other point of view, what point is there arguing with someone whose inherent philosophy is a denial of the rights of others?
An example of this is the one that you used. The "alt-right": people who follow the words of leaders who have clearly and openly called for the extermination and sterilization of PoCs (Richard Spencer, for example), people who openly use Nazi imagery, and who are backed by the American Nazi Party. [Evidence for these claims are in the bottom section].
In such a case, with the sides, quite literally, being:
I wish to live and have a productive and happy life
I wish for people like you, including you, to no longer exist
What kind of meaningful debate do you expect between such groups? The core principles are, by their very nature, severely opposed to each other.
[Citations for the equivalence of the Nazis and the Alt-right]:
Firstly, Richard Spencer, the person who started the alt-right:
""Instead of asking how we can make reparations for slavery, colonialism, and Apartheid or how we can equalize academic scores and incomes, we should instead be asking questions like, "Does human civilization actually need the Black race?" "Is Black genocide right?" and, if it is, "What would be the best and easiest way to dispose of them?" With starting points like this, wisdom is sure to flourish, enlightenment to dawn. ""
https://web.archive.org/web/20120216183528/http:/www.alterna...
http://rationalwiki.org/wiki/Richard_Spencer
https://twitter.com/IGD_News/status/890979293009895424
See also:
https://www.nytimes.com/2016/11/21/us/alt-right-salutes-dona...
https://www.adl.org/education/resources/backgrounders/alt-ri...
http://rationalwiki.org/wiki/Alt-right
https://www.splcenter.org/hatewatch/2017/07/26/neo-nazi-misf...
There are more, but I'm pretty sure that you can source the rest for yourself.