The 'Kenosha Guard' were formed in response to the George Floyd protests, so race can't be excluded here as a contributing factor in the formation of the militia. There is also evidence that the Boogaloo Boys formed at least part of the militia, who can be generously described as 'white-supremacist adjacent'.
On the day of his 'not guilty' plea, he met with Proud Boys in a bar, and was caught displaying the 'OK' symbol on camera.[0] I don't have anything nicer to say about the Proud Boys than the Boogaloo Boys.
This wasn't admissible at trial, but is nevertheless true, and leaves little doubt in my mind that Rittenhouse is a white supremacist, or at least associates with white supremacists.
I think it's important to remember that these events didn't occur in a vaccuum, and the backdrop of the protests/riots/unrest/whatever you want to call it is one of the shooting of a Black man in questionable circumstances, so which 'side' you are on is important.
[0]: https://www.washingtonpost.com/wp-apps/imrs.php?src=https://...