I disagree. Mandatory sentences are a bad idea and end up with too many largely non-violent people in jail, when the crime can be addressed by more appropriate penalties. We don't need more people in jail.
It's also tricky...at what point are we infringing on the rights of free speech and assembly? My point is property destruction, assault, and impeding a person's ability to move from place to place. But not all require stiff penalties.
For example, consider this:
'Bubble' laws protect patients and protesters alike