Who'd athunk so much misconception could surround any issue.
First off, they are British citizens, not US citizens. So the US is under no obligation to protect their rights, regardless of what you as an individual might think the origin of those rights are. We die in enough piss-holes around the world while protecting those rights for some people without committing ourselves to dying in every piss-hole where somebody says something that offends somebody else. Not that I think Britain is a piss-hole, in fact it is one of the few countries I would be interested in visiting some day. But establish 'protecting British citizens from their government' as a US responsibility would, at least if consistently applied, lead to us doing so for all the piss-holes around the world as well. Frankly given the gratitude we've gotten for doing so recently, I've had enough of that.
Next up, they did break the law when they came to the US, so their incarceration was entirely appropriate. They attempted to enter the country under false pretense, which is a crime. My problem with the conduct of my government on this issue is not how they handled these two people, but their failure to apply this solution more even-handedly in protecting the integrity of our borders.
As to the issue of whether or not they ought to be incarcerated in Britain I would say there are several competing interests here. First off, on a moral basis I do quite think they will eventually get what's coming to them, and that some number of years in jail is a mere down payment on their eventual punishment. But I hold that punishment will be delivered in the hereafter, not the now. In the here and now, I prefer a government which does not imprison people after the fact for extended periods of time for exercising free speech. I'm not sure there are actually any of those left in the world. As a practical matter, they have been tried and convicted by a court that I deem to be as reasonably constituted as can be expected these days. Therefore the trial itself is lawful, as is their conviction under it. Now as to the wisdom of that law... It seems to me that per capita, England in particular and Great Britain in general, has more Jew-hating radicals than the US, although it likely has somewhat fewer than Europe. At least some of these people have already been locked up in the same prisons to which these two scumbags are headed. So the odds are fair that two run of the mill racists can be radicalized into more effective terrorists than they already are. Only this time profiling, which is otherwise actually a decent tool for a first approximation on determining who the bad guys are, will be of absolutely no use. Welcome to The New Jihad.
Grenade, because pretty sound carrying guns won't be enough.