I am not sure what we should have done about Hitler. I think about the millions gassed and the effects of the bombs on Hiroshima etc. and wonder whether we achieved much by going for all-out war. That is apart from all the people, both German and on the allied side, who were bombed out of their homes and killed in their beds.
Might we not have better used our intelligence services to find a way of targeting Hitler himself? To have put all our eggs in that basket as the best way of destroying the threat? If all the massive effort that went into the war had been focused on this one aim I am sure it could have been successful. What would have happened next, who knows? Clearly it was not possible to negotiate with him; but I am willing to bet there were those in his entourage who would have been amenable to cooperating in wiping him out.
Equating this situation to WW2 does not really help us - the outcome of all-out war this time around would be very very different; and far far more dangerous.
As to Syria, unfortunately we will give hope to the rebels by actions such as Trump's. That is not the aim; but it is the result. If the rebels have got any sense they will now be trying to find ways to engineer further chemical attacks, however small, so that they can get Trump to do their dirty work for them.
It is very complex, there are wheels within wheels, and just dropping in from above is a huge sledgehammer reaction.
I in no way condone the chemical attacks - who in their right mind would? - but we really do have to tread carefully and I have no faith that Trump has the remotest idea about such a concept.