The userboxes aren't templates, so they don't fall under T1. The US has nearly total protection of free speech, so espousing beliefs, even Naziism, isn't illegal.
As far as I am aware, neither Wikipedia nor the Wikimedia Foundation are the United States.
True, Wikipedia can have rules in addition to the law. However, what are discrimination laws like in the US? Could banning Nazis get the Foundation into legal difficulties?