At the same time, i would presume if his arrest was this irregular and illegal he would be taking it to actual court instead ofthe court of public opinion.

Are these exclusive opportunities? I'm not familiar with danish law.

Not exclusive, but in general its a bad idea to post on social media if you plan to take it up in court, as its very easy to accidentally say something that shoots yourself in the foot.

I suppose. I don't think that matters much in places with functioning legal systems.

It's the other way around.

In a functioning legal system it matters what you said or didn't. In a non-functioning legal system they will just convict you regardless of what was said or done.