It really isn't.
I posted this on the other thread but it is relevant here:
There are violent extremists on both the extreme right and extreme left wing - and let's face it, political opinion is basically a circle with not that much of a gap between the extremes on both sides.
Of course those on the left are obvious suspects when it comes to violence against politicians on the right and vice versa - although the data is clear that right wing extremists are responsible for a lot more acts of violence and terrorism than left-wingers.
www.cato.org/blog/politically-motivated-violence-rare-united-states
This data shows that if you exclude 9/11 there have been 477 politically motivated deaths with the right responsible for over 80% of them and the left responsible for 14%.
And before anyone shouts bias, the Cato institute is libertarian, so generally right leaning.
In the UK, the majority of political killings in the 20th century and beyond were driven by the Northern Ireland Troubles and were commited by the IRA on the left and the Loyalists on the right.
There has been no other left wing politically motivated killings or attempted killings in the UK as far as I can recall - they have all either been Isalmist (05/07, Lee Rigby and David Amess) or right wing (Jo Cox).
There have been three potentially political acts of murder or attempted murder in the US in the last couple of years which have been 'linked' to the left.
I say potentially because none have been confirmed as being politically motivated.
Trump assassination attempt - deemed left wing because the perpetrator once do ated $15 to the Democrats, even though he was a registered republican and had a social media account which tended to lean towards right wing views.
The Minnesota church shooting - deemed left wing because the perpetrator identified as trans and his journal had one entry with a rainbow flag and a mention of equality but beyond that, nothing known about his motivation other than he was obsessed with other mass shootings.
Charlie Kirk - perpetrator assumed to be from the left but we don't yet know and Kirk was disliked by a lot of people on the extreme right due to his willingness to debate the issues and not just impose his views.
Happy to consider the view that there are a lot of violent extremists on the left if it can be backed up with data - but I can't find.anything which suggests that this is the case or that the left are more violent than the right!
*Addition - I have also just remembered the assassination of Brian Thompson - but the perpetrator in that case was neither right wing or left wing as he held a mix views.