The reality is that a significant minority of Brexiters share the same sentiments as Thomas Mair, that is: left leaning, white politicians have 'betrayed' the country. They are 'traitors'. You see these people in the comments sections of articles, forums, and social media. Let's not deny there are many unsavoury, bigoted, and borderline racist types who support Brexit.
As an undecided voter who greatly values the pro-democracy argument of the Leave side, the idea of voting alongside and empowering people who share such disgusting views leaves me feeling really uncomfortable.