He's an idiot who, seemingly, talked and walked himself into a guilty verdict.
First off, he wasn't arrested/charged/convicted of 'Hate Speech'. I don't know why every single report insists on claiming he was. Or for a joke, for that matter.
He was arrested and convicted under Section 127(1)(a) of the Communications (2003) Act which specifically states that sending a message that's grossly offensive over a public electronic communications network is a crime. That's what he was charged with. You can have any opinion you like, you can make any joke you like, just don't fire it across the internet or down a telephone line.
Important Sidenote; A point that a lot of people discussing this completely misunderstand. Grossly offensive is not a measure of the level of offence caused or taken. It's not a courts joke to weigh up which message before them is more or less offensive than any other. It's not the extreme version of Lightly offensive.
Grossly offensive simply means that something can be held to be generally offensive to public sensibilities, as opposed to extremely offensive to any given individual/group. This is a binary decision. Under current prosecution guidelines there doesn't have to be an identified victim for there to be a successful prosecution - once the court has decided that the video (or whatever it may be) is grossly offensive it moves on to what you done with that content was reasonable.
In the beginning I think the prosecution had an extremely flimsy case. They had a guy who by all accounts was just a stoner nerd, no history of crime, no history of bigotry etc and a video wherein he makes a really ill considered and dumb joke.
Their main argument was to sow doubt in his character, that perhaps it wasn't just a joke to say "gas the jews" 23 times to a dog and upload it to the internet. He doesn't appear to be a dumb person, he should be perfectly capable of understanding why it might be beyond the pale to broadcast that content out to the world.
That's why they argued that context was irrelevant. Not because they just want to cut out little snippets of phrases from the middle of a sentence and go gotcha bitch, get in the cage; but because repeating the same distinct phrase (with the historical contexts it has) to the dog on the premise that the whole video is a joke might be stretching context a little.
If a person produces an hour long song but right in the middle of it repeats the phrase "kill n\ggers*" 25 times, then continues on with the song - is saying that it's contained within an overall artistic piece a legitimate defence? Maybe it depends on who made the song.
Anyway, It's at this point the vast majority of defendants would apologise, accept that it was a mistake it had gotten that far, offer to (or show they already have) remedy the situation and offer up some kind of character witness to explain how they're a good boy. You know, show a little contrition. Even if it's fake as all hell, you do what you got to and avoid the conviction. Then later use your story to campaign and change the law.
Dankula did some of that. He did apologise for any offence caused and he did eventually take the video down. However, he didn't appear to show any real understanding of why it could be considered grossly offensive, why the law distinguishes between public and private messages; and chose to basically launch himself full force into the waiting arms of people like Alex Jones, Lauren Southern and Tommy Robinson.
Should he be guilty by association? No. However when your prosecutions flimsy case rests on you perhaps not being as dumb as you look/act it's probably not the best idea to help prove their point by becoming the willing martyr for conspiracy theorists, 'identitarians' and ex-EDL leaders who all quite openly used him and his case to further their own agendas.
Don't get me wrong, it really probably shouldn't have ever gotten this far. He shouldn't have been arrested, he shouldn't have been charged, shouldn't have been convicted etc. It's been a colossal waste of time and money.
Once it did all happen though - as sometimes happens in law, zealous prosecutors will sometimes just pursue anything and everything - Dankula created a road map for exactly howto turn a certain win into a massive upset.
I hope he doesn't get jail time, I hope he doesn't get a large fine but if he does; Letter of the law made it possible, actions of an idiot made it probable.