Some seem to be reactionaries, essentially trolls who may or may not truly believe the anti-Semitic and racist bile that they meme and share to get a rise out of the politically correct left. If youthful rebellion in the 1960s meant embracing free love, peace and equality, then today — at least for anti-anti-Trumpers — it is about promoting hatred and structural inequity.
Others may genuinely wish to burn the whole system down.
It is a flawed system, after all, one whose recent financial crisis irreparably scarred millennials’ economic prospects. Most anti-establishment millennials have drifted toward leftist populist alternatives, but some have sorted into the opposite (and more violent) extreme. For right-wing populists, the key flaw with the system is not that it allows the rich to hoard all the money, but that it privileges undeserving minorities at innocent whites’ expense.