The problem here, as I wrote above, is arresting a UK citizen in the USA. If they would've issued a warrant and the UK police decides to arrest him and then extradite him, that's fine.
But this sort of thing... this could potentially halt international travel. I am not kidding: how do you dare to travel anywhere if you can be arrested for something you did years ago which very well might have been legal in the country you resided in but not in the country you travel to?
What Malwaretech has been charged with here would likely be illegal under UK law as well as US law (section 37 of the Computer Misuse Act [1] appears to be analogous to the charges being brought against him). And regardless, the UK-US extradition treaty is written in such a way that the US charges do not have to be illegal under UK law for an extradition to take place (although the converse is not true).
Now, it may well have been the case that when the inevitable court case to challenge the extradition in the UK took place, it might have gone all Gary McKinnon on them [2], due to public support after WannaCry etc. which I'd suggest is probably why the FBI chose to arrest him in the US rather than put in a formal extradition request or work directly with the UK authorities (AFAIK).
But yes, I do agree that with the advent of a worldwide communications network, travel to countries with oppressive, obscure, or stricter legal regimes has become more dangerous for some. The thing I find curious is that others haven't perceived this change in risk.
I wouldn't necessarily say this is a bad thing either - note there have been a number of (accused) botnet operators/cyber-criminals originating from Russia who were arrested whilst holidaying in the EU, and then extradited to the US. Since Russia has a reputation for being lax about prosecuting such "crimes" (especially if they only target people outside of Russia), and also tends to refuse to extradite Russian nationals, it doesn't seem that there are many other options.
Why is it a problem that if you commit a crime and then visit a geographic location where the local governing entity has jurisdiction, you could get arrested?
If he had robbed a gas station in Las Vegas, would you be upset if Las Vegas police arrested him?
Do you believe that "I am not a citizen of your country" automatically provides exemption from a country's laws even when on their soil?
If I went on travel to a foreign country and committed a crime, I would expect to be arrested there. Where the damage was done is the key, not where I was at the time. If I create some malware that takes out UK servers, I would expect to be arrested for that if I ever set foot on UK soil.
If you ever posted a sickle-and-hammer to the web, visible to the Hungarian public -- distributing it -- then you possibly could be fined for it. If you visit Hungary and you got fined, would you consider it just? Here's the Hungarian Criminal Code article in question:
Article 335(1). Any person who
a) distributes;
b) uses in public;
c) exhibits in public;
a swastika, the SS sign, an arrow-cross, a hammer and sickle, a five-pointed red star or a symbol
depicting the above, – unless a graver crime is realised – commits a misdemeanour, and shall be liable to
punishment with a fine.
(2) The person who uses a symbol of despotism for the purposes of the dissemination of knowledge,
education, science, or art, or with the purpose of information about the events of history or the present
time shall not be punishable.
(3) The provisions of subsections (1) and (2) do not extend to the official symbols of states in force.
As I've already noted, Germany and other countries have enforced their no-Nazi-stuff laws against US-based entities.
If you do a thing that's illegal in Hungary, and then put yourself on Hungarian soil, I'm not going to be surprised when you get arrested. In other words, this is not the knock-down "that'll really show him!" counterexample you're looking for.
This seems untenable. Now, to travel to another country for holiday, I need to look back on everything I've ever done, (even something so minute as distribute an image of a hammer and sickle) and pore over the laws of that country and determine I have not ever been in violation of _any_ of them?
I don't think most people would say that's how it should be, it's just the way it currently is. Law enforcement typically does not care about your convenience.
But this sort of thing... this could potentially halt international travel. I am not kidding: how do you dare to travel anywhere if you can be arrested for something you did years ago which very well might have been legal in the country you resided in but not in the country you travel to?