I saw a lot of posts about this case from the UK so I looked into it. This guy wasn't jailed simply for opposing immigration, his stickers promoted a website that explicitly called for "Racial Holy War," contained a bunch of slurs (n-word etc), and seemed to be some sort of weird religious cult.
Doing things that are transparently illegal when you live in a dystopian Soviet country like the UK is very dumb. If your country has "hate speech" laws, you shouldn't touch people like this with a ten foot pole, they're liabilities at best.
Of course European governments are immensely corrupt and people who post mean words online shouldn't receive harsher punishment than violent criminals. But you can make this case more effectively by citing clear-cut examples of anarcho-tyranny. The public is more likely to sympathize with somebody who got arrested for quoting a biology textbook than a guy in a cult who called for "Racial Holy War."