To varying degrees, yes. Who else can be held responsible? Just the people that were directly involved? Why is okay to kill a boy who has just been conscripted into the army, but not okay to kill an adult who knows full well that the bombs that he's making will be used to murder civilians?
but this definition means that
anyone is a legitimate target - whether that be women, children, the infirm or ther elderly.....
you're talking yourself round in circles on this one. The allies employed women to work in factories to support the war effort in the same way the germans did.
So the allies were justified in bombing german civilians because the germans bombed the allies' civilians
and the germans were justified in bombing the allies' civilians because the allies bombed the german civilians.....
They don't target civilians
you didn't make a distinction over "target" with your original post...
By supporting a government that bombed enemy civilians, they tacitly gave permission to be bombed themselves.
but, if you want to shift the goalposts

......
it all comes down to semantics over "target." But certainly in WWII, both the allies and the germans conducted bombing raids whose main casualty was known would be civilian. The decision to drop the atomic bombs over hiroshima and nagasaki, or the firebombing of dresden or tokyo were all actions for which civilians rather than the military were targeted.
I'll carry on with the israel example, the IDF are responsible for the death of civilians in so far as these deaths are a recognised and accepted consequence of their targeted actions.....
indeed, any military force in war accepts "collateral damage" as a consequence of their actions.
So to argue over "target" is to argue over responsibility. You seem to be arguing that only if civilians are directly targeted that there can be any responsibility. But what if actions are undertaken for which there is an acknowleged likelihood of civilian death as a consequence? Where does the responsibility lie then? This rationale still leaves us with the argument that civilian deaths are acceptable for the greater good.....and if so, your catch all
By supporting a government that bombed enemy civilians, they tacitly gave permission to be bombed themselves.
still applies to whoever wants to use it - whether that be WWII Britain, the IDF, or Hamas.
and it's a very dangerous path to go down....