The four-hour occupation of Interstate 94 on Saturday night that left more than 20 officers injured was a frightening illustration of why Minnesota and the nation as a whole must find a different way to deal with race relations, which now are heading down a dangerous path.

Protesters have a constitutional right to peaceful assembly. They do not have a right to block roads. It’s that simple. While the restraint shown by local law enforcement is admirable, protesters crossed a line that should have been enforced with the very first venture onto a freeway or rail line.

Now the unlawful actions must stop, before the next “occupation” ends in tragedy.

It must also stop because it is ineffective and threatens to backfire on a movement that is needed as a motivating force for changing the status quo. The death of Philando Castile was a wake-up call for many Minnesotans who only now are realizing how very different day-to-day life is for some in this state.

The Black Lives Matter movement has galvanized public attention. Footage from Saturday’s protest showed a crowd that was young and old, white and black, linked in common purpose.

But without a constructive plan, such movements can deteriorate into chaos and violence.

That can’t be allowed to happen here, because we need the change that activists seek, and it is needed on many levels.

News of the shootings of Philando Castile in Falcon Heights and Alton Sterling in Baton Rouge, La., and of the five slain police officers in Dallas, has brought out the best and worst in Americans. We have witnessed men and women of goodwill coming together in ways not seen since the civil-rights movement. But we have also seen rage and racial hatred on both sides that bode ill for this nation if we cannot, at long last, reconcile our differences.

The problem is far greater than just disparate law enforcement. There is too much evidence in this country of systems that remain tilted against racial and ethnic minorities, whether it is education, employment, criminal justice, homebuying or banking.

What will it take to finally root out prejudice and racial injustice in a country that began its life enslaving part of its population? That is a question too broad for any single editorial. But we know that the happy talk of a “post-racial” era that some indulged in with the election of this nation’s first black president was poppycock. In some quarters, bigotry has, if anything, grown bolder since those heady days of 2008.

There has been much progress in this country since the days of separate bathrooms and overt segregation. But let’s not pat ourselves on the back just yet. The obstacles that remain are insidious, often masked by a veneer of diversity and good intentions. Unless this community, this state, this country, commit to a truer equality and refuse to settle for surface improvements, there will be no real justice. And, most likely, no real peace.