It seems that both justifications have been used. https://en.wikipedia.org/wiki/Activities_prohibited_on_Shabbat#Igniting_a_fire https://en.wikipedia.org/wiki/

It seems that both justifications have been used. https://en.wikipedia.org/wiki/Activities_prohibited_on_Shabbat#Igniting_a_fire https://en.wikipedia.org/wiki/Activities_prohibited_on_Shabb... "Many poskim ground their prohibition of operating electrical appliances in this melakha."