The difference is they were protesting unjust segregation laws. The problem with this is that it being illegal to block an interstate is actually a pretty just law[.]

https://en.m.wikipedia.org/wiki/Selma_to_Montgomery_marches

These individuals were marching in the street — presumably, blocking traffic — all the way back in the 1960s. Blocking traffic/disrupting commerce/demonstrating in public spaces has a long history in America, and, even if that specific act did not, civil disobedience is, by definition, a violation of the law.

[These laws] aren't unjust at all. Stiffening the penalties attached isn't racist or unconstitutional, it's a public safety matter.

No. They aren't.

And no one is saying they are unjust. What is being said is that civil disobedience should not be made into criminal disobedience, simply because it is inconvenient.

Much has been done in the name of public safety that is fundamentally a restriction and/or abridgment of our rights as citizens.

However, if you're truly worried that emergency vehicles won't be able to attend to their business, then what if the protesters agree to leave one lane open for emergency vehicles? Would that satisfy your concern?

It's not safe for people to block major interstates at rush hour.

This seems a bit unfounded. As long as emergency services remain uninterrupted and/or there are alternate routes available to travelers, surely there is not such a pressing public interest that the rights of citizens to demonstrate and assemble (as enumerated in the constitution) need be further restricted.