I hate that "poison gas" quote. It is always taken out of context, and it is just a cheap kind of character assassination because it sounds like advocating for deadly poison like mustard gas, when in fact it was humanitarian idea: using tear gas instead of artillery shells. You could say Churchill wanted to invent modern tear gas type riot control instead of actually murdering people. Which is a humane thing IMHO.

"It is sheer affectation to lacerate a man with the poisonous fragment of a bursting shell and to boggle at making his eyes water by means of lachrymatory gas. I am strongly in favour of using poisoned gas against uncivilised tribes. The moral effect should be so good that the loss of life should be reduced to a minimum. It is not necessary to use only the most deadly gases: gases can be used which cause great inconvenience and would spread a lively terror and yet would leave no serious permanent effects on most of those affected ... "

Statement as president of the Air Council, War Office Departmental Minute (1919-05-12); Churchill Papers 16/16, Churchill Archives Centre, Cambridge.

Note: lachrymatory gas = tear gas.

(I am not sure about he rest but it largely can be summed up as racism, which was fairly normal in that age. While mass murder is an absolute evil in every age, racism without the explicit intent to do large scale harm is more of a cultural thing, a relative thing: it was basically normal back then. We condemn it now, but then again we too believe in things people in that age would condemn. There is hardly any historical figure who never agreed with ideas that today would be seen as horribly racist or homophobic or misogynist or stuff like that. Cultures and morals change.)