Where do you deport them to though? Can't send them back to Syria, it's a failed state and they'd be handed back into the custody of those they ran from. This would likely mean torture and execution.
Which yeah they tried to set a dude on fire and I can see the emotive well they deserve to be tortured and executed answer forming in people's minds and I do understand the need and want for bloody retribution but I would hope a cooler head would see why this isn't really an option
I imagine that general EU law is the same as in Sweden where you first try if the country in question is safe (according to migration office praxis), then you try the first Dublin Country (as neither Germany nor Sweden has an obligation to accept refugees that didn't arrive there first). Even then (in Sweden) the crime needs to be severe and there needs to be a risk of further crimes or a threat to national safety. If no country accepts then you'll serve time within the national criminal justice system.
What gets a lot of people angry in cases like this is that most civilized states won't deport people to severe risk of death, torture, and other uncivilized violence (like in Syria), and can't accept that no matter how severe the crime we actually don't have capital punishment and value even the lives of all criminals. Not that they'd wish death for EVERYONE, just that, you know, certain people should be considered, maybe?
So yeah, everyone asking for deportation to war torn countries is asking to break national and EU law. If it's safe to deport to said country, and a person commits a crime, it's generally possible to deport an adult and you don't need to rage about it. If a person supports killings for crimes then that's not really something that rolls in the EU and maybe they should find someplace else to live.