This is not about some general vague problem with "extremism" of which supposedly all sides are guilty. This is about the emergence of an Islamic terrorist movement which has already committed several attacks. When your first reaction to this is to to bring in some unspecified crimes of the US, then this calls into question whether you understand the seriousness of the situation. There is a real chance that real, actual radical Islamists kill many more people and perhaps even gain more political power. We can talk about this without engaging in some false equivalence.
"Trump has not denounced white supremacist terrorism" is the equivalent to "Obama has not denounced radical Islamic terrorism".
It's a media trick used to derail any conversation about whatever the president is trying to get done and make everybody talk about something incendiary for a while.
There is no useful policy anybody is going to put in place against fascism that hasn't already been there since World War II. Terrorism is already the most illegal of things. Do we really need to encourage Republicans to pass another law against terrorism? One Patriot Act is already too many.