We’ve seen a lot of questionable use of the terrorist label since federal law made it extremely significant after the 911 attack. Internationally, labeling groups as terrorists has become a tool of US foreign policy that is not always connected to either justice or actual terrorism.
I think you’re very wise to point out the domestic risk. Expanding the definition of terrorism risks catching people up in powerful federal laws that were designed for much more limited use.
The people most likely to be hurt are minority groups. We should move very cautiously in this area.
Were there people involved in the attack on the Capitol who met the classical definition of terrorist? Very possibly. But it strains credulity to imagine that most everyone who went to Washington DC to protest met that definition.
Those who committed crimes should be prosecuted and pay the consequences for their actions. But it isn’t necessary for us to legally brand them as terrorists in the process.