lol. Really? I laughed out loud at this one :)

Why?

Again, you're criticizing local law enforcement for not doing a thing, but not explaining why or how they should do the thing. From what I can tell from looking at Google Maps, the ICE building is generally flush with the sidewalk along most of the property lines. The areas where it's not are almost entirely devoted to the main driveway and the entrance courtyard into the building. There's nowhere I can see that you could put a barrier that would be effective to keep out protestors without making the building unusable. Or did you have a suggestion?

Next you’ll tell me that they might try to break into the ICE building, throw fireworks at offices and physically assault them.

If you 10x the number of people at the protests, then that's more likely to happen. But if you let the people who aren't breaking into the ICE building or physically assaulting agents just hang out and do their protesting, rather than try to suppress the protests, you'll have far fewer people.