don't have legitimate grievances
there are no legitimate grievances that justify their ideology. That's a different claim than the one i'm making.
They don't become bigots because the evil leftists forced them to either.
sure. But 1. racism and prejudice aren't there/not there things (indeed there are multiple things in both of those terms which we generalize into one). We're all prejudiced in some ways and no all prejudices are bad (we just define the term as "the bad ones"). Someone who could slip through the cracks into deeper and more vile fascism, white nationalism, etc. can be called to the better angels of their nature and have those passions siphoned off to more productive beliefs and actions. A lot of vile white supremacists will be impervious to any sort of real solution but they may be responding in part to similar problems less vile people are.
To claim there are no legitimate grievances means you're also saying non racists don't have legitimate grievances or disagreements with an orthodoxy. E.G. Amartya Sen is a brilliant Indian (Bengal) economist/philosopher who has deep critiques of identity politics and what we often call multiculturalism. You don't have to be a noble prize winner to distrust our current mode of identity politics under a similar, if less fully thought out, manner. Xenophobia is often linked to conditions at home. you can criticize the xenophobia or say that hatred is misdirected but the very nature of the term misdirected means there is something there they react to. Take Europe: there has been a huge multidecade failure to integrate minority (often arab or black muslim) populations with horrible results. The far right gained support because they saw this and reacted to it. They may have seen it and said something because of bad opinions x y and Z but what they were reacting to was objectively true and mainstream parties didn't want to consider it.
Just look at something like Rotherdam. does that happen in a society where there is an ability for mainstream politics to have a healthy amount of skepticism of immigration and naturalization?
it's not stormfront or you're ok. People do drift. to take breitbart's taxonomy, perhaps you shift towards somewhere like VDARE and while you don't really agree with many of their racial claims, repeated exposure makes it seem less outlandish over time, or the general ceding of cultural conversations over culture and gender/personal identity can get people into seeing a false dichotomy between red pillism and "SJWers." A lot of people do reject the image or images of "non toxic" masculinity/the destruction say of the "masculine gender role/"patriarchy" (taking that word for word from geek feminism wiki) but that's not the same as being pro red pill, unless one doesn't perceive another option.