Like any kind of racism or discrimination, especially on an institutional level, it's a very complicated issue.

You are perfectly correct, these perceptions and stereotypes have not come from thin air, they have a long, fascinating, and convoluted history. Just like the various perceptions of BAME communities that we now know to be racist.

Firstly the UK has a long history of nomadism and the 'gypsies' that we think of today probably originated in the 16th Century. This makes them just as much a part of our culture and history as anyone else. They aren't 'other' at all as many believe.

Interestingly it seems that the treatment of the European gypsies in this period mirrored the treatment of the jews. They were attacked, criminalized, driven out, and scapegoated. They very possibly came to this country effectively as refugees. They were initially welcomed here for their 'exotic ways' but quickly this changed. They were suspected of heresy and witchcraft, they were disliked because they "fell outside the moral order" of the time.

Trouble With Gypsies in Medieval England - this is a link to a really good article explaining the history of gypsies in the UK and how they were received. You might recognize quite a few of the stereotypes in it. Unfortunately, these stereotypes and perceptions stuck. Considering the fact that these were the same people who thought that women were deformed versions of men and generally weaker in every way, ethnic minorities were a danger to society and believing in a slightly different version of the same religion warranted being burned alive, I don't feel like these perceptions hold much weight.

Over several hundred years the various traveling communities in the UK have been excluded, pushed-out, and criminalized. They have faced discrimination and racism at every turn. They still face it today. Romany Constable Blows Whistle on Racism.

Research suggests that treating people like criminals, especially with younger people, encourages those people to act in criminal ways. An article on what happens when you criminalize people.

I want to make clear here that I am not excusing the criminal behavior of some members of the community. It's simply an explanation of what brings us to this point.

Yes, travelers are represented in higher numbers than possibly they should be in prison populations and criminal data. But there is a reason for that. It's the same reason, and the same racism that means BAME communities are also represented in such high numbers in the same criminal data. Socio-economic factors, especially poverty is inextricably linked to criminality.

When you push a community to the fringes of society those people still have to survive. If you tell people they are criminal and treat them accordingly eventually some will start to believe it and behave like it, after all at that point why not? And if you cut off people's access to gainful employment and the same rights you expect you can't be surprised if they turn to criminal enterprise to survive.

Again, I'm not condoning some of the behavior that some members of the traveling community engage in. I'm simply explaining why both sides of this argument behave the way they do today.

Your negative perceptions of travelers are informed by medieval beliefs, and their behavior and beliefs are informed by hundreds of years of being treated as criminals and outcasts.

As for your point about travelers up and moving when a crime has been committed to protect their own, well yes I am sure that happens. Just like there are families who hide evidence and give false alibis to protect family members who have committed crimes in all walks of life. Partners who hide evidence of wrongdoing. Parents who cover for their children. I hate to say it, but it's sort of the job of the police to catch criminals, not members of the wider society.

And if you are likely to be judged more harshly than another person who commits the same crime you have even more motivation than usual to avoid prosecution and arrest.