I don't think anyone on here has said that the perpetrator deserves more sympathy than the victims. That would be bizarre. Of course it must have been terrifying for everyone on the train, the physical and psychological injuries inflicted must be horrific. The police obviously had to kill him.
Some people are recognising that he was human too and saying that it is possible to have compassion for everyone involved when something awful happens. Happy and balanced people don't commit atrocities. (Not every traumatised person attacks people, of course, people deal with things differently, some internalise their trauma and deal with it in different ways. )
I met someone caught up in a similar attack a few years ago. She had sympathy for her attacker who had been seriously let down by mental health services.
Since when has having humanity and compassion been left wing? That's really sad if you believe right wing people can't have empathy and sympathy.
Also, how progressive is it to see the world as "good vs evil"? That is so backwards! It's a massive over simplification and contributes to why we are in this mess. No one actually sees themselves as the baddy, they see themselves as "heroic" or as "freedom fighters" or "having no choice" - that's the problem and spouting more fear and hate on here will not sort that out. It is only through understanding that these atrocities can be prevented.