First of all, no one deserves to be executed for their political beliefs. That needs to be said loud and clear. That guy has a family whose lives have been turned upside down. I think of them right now.
However, there is a wider question here, and it is one that the Right (and it is the Right) must confront themselves with.
And that is, when governments keep shifting the Overton Window to the Right (as has happened gradually across Western society in the past 45 years, particularly here and in the US), when Right-leaning billionaires buy up newspapers and TV channels and apply Right-leaning editorial policies, when Right-leaning governments try to shut down certain types of protest whilst allowing others free rein (contrast the treatment of Palestine Action vs, for example, farmers, who were allowed to bring central London to a standstill last year), when Right-leaning governments spew hate into the atmosphere like they do with the language around immigration, when you do all of this, when you attempt to have two different sets of goalposts (one for the Left, one for the Right), then don't be surprised if that gives rise to nutjobs who are going to find a different and violent way to make their voices heard.
To be clear once more - I am not trying to legitimise or excuse extremism/terrorism, I am simply saying that you shouldn't be surprised to be on the receiving end if you are directly contributing to the conditions that give rise to it happening.