I said it eleswhere but this assasination attempt is almost certainly not related to spanish politics. The guy is retired and hasn't been in office since 2014. He still is active as a lobbyist for the ‘National Council of Resistance of Iran’ and ‘European Friends of Israel’. He is also considered a terrorist by the Iranian government. So if this is politically motivated, it's way more likely related to the current events in Israel.

Accepting violence as a valid political tool for anything other than an absolute last resort is the exact thing that leads to complete and utter chaos. You have to keep in mind that your side is probably not the only side with guns, and those on the other side are also telling themselves that there are plenty of examples of what happens when you let communists get comfy.

Now, I would obviously say that one of these sides is much more in the wrong, but that doesn't change the fact that, unless you want a politics of everyone shooting at each other, political violence should essentially always be condemned, even if it's against your political foes.