That's one example.  Same thing happened with D's voting for Trump in open primaries last year.  It's not really anything new.  Voters in both parties have been doing this for decades.  

The difference now is that Colorado's stupid new law makes it so much easier to do, and thus we're likely to see a lot more of it.  Within 10 years, I expect over half of the state to be registered as (U) as they figure out the tactic (if that law doesn't get rescinded).

It's also going to play havoc with polling.

And yes, I voted against it for the same reason. Parties exist for a reason. Want a say in a primary?... join that party.

But I also changed my registration to (U) a week after the election. I don't like the law, but since it IS the law now, I'd be a chump to not take advantage of it, knowing the other side will.