Well, in this case, it was clear that the choice was between Communism and military totalitarist regime/falangism/Fascism:

There was a failed coup by the PSOE and left-leaning political groups in 1934: https://en.wikipedia.org/wiki/Revolution_of_1934

They failed and the next two years were a sequence of minor scale violent events that ended in a war in 1936. Of course, the coup by the military forces is not justified, but the caotic situation made them choose what they thought was the "lesser of two evils".

I’m not justifying the coup. Once the war started both political extremes believed they had the mission to prevail whatever it took. That’s why it became a Civil War and the end of the Republican Spanish State as the way to keep law and order. That’s when the butchery began. The Civil War atrocities came when the Republican Spanish State collapsed and a plethora of “experiments” started to pop up around the country driven by local communist, socialist and specially anarchist leaders trying to do the revolution on their own. The atrocities from the National (rebel) faction started from day one of the coup and they were driven by a centralized and unified alternative “national state” that prevailed because it was better applying law and order, even having very low support from the Spaniards. The Anglo journalists and writers saw how some of these “experiments” worked. It’s not strange to see how they enthusiastically supported it at the beginning and how they changed their mind of even became critic with socialist mindset.

> I’m not justifying the coup

Painting both sides as equal, when one was democratically elected, and the other a military coup is extremely inaccurate, to the point where it suggests some strong biases. My guess is this is why it comes accross as you justifying the coup. Edit: quote