Then maybe an ad-hoc time-critical gathering shouldn't be on freeways in certain locations (sincere, not trying to beg-the-question)? Gathering in a location that presents a danger to themselves seems like the ideal situation where we need to examine it closely and not make blanket statements as to whether it is okay or not.
I'm not really espousing a particular position, just that we should think critically about this and realize that the act of using a freeway for a parade and for protest aren't always all that similar (but they may be, it really depends).
From the point of view of the 1st Amendment rights to freedom of speech and peaceable assembly, I think they should be treated as equivalent. Both are political speech, and the government must not favor pro-status-quo speech (like a 4th of July parade) over anti-status-quo speech (like a protest march).
Indeed, if they're going to favor one, I'd rather it be the anti-status-quo speech. The US is founded on the notion that we are always seeking a more perfect union. The reason the Great Seal [1] has an unfinished pyramid because we should never think we are done.
I don't disagree with this, it's actually a portion of the point I was trying to make. That is, all other things equal, they should be equivalent. It's the "other things" here which may make the results different, and I'm not sure that's a bad thing.
For example, consider a parade scheduled from 11 AM to 1 PM on Sunday, known well in advance, and an impromptu protest that really gets way at some random point in the afternoon, most people didn't know about, and causes logistical problems for many people. I value and appreciate the need for both, but I also understand and support the police trying to contain and in some cases disperse (peacefully!) the second. Indeed, the anti-establishment bent the protests often have usually benefits from some police presence, IMO. It's a better story and reaches more ears.
I'm not really espousing a particular position, just that we should think critically about this and realize that the act of using a freeway for a parade and for protest aren't always all that similar (but they may be, it really depends).