It's incorrect to assume that the whole world was firmly united in opposition to the Nazi's, both American and British societies were deeply divided on the issue.
There were liberals around back then too.
By 1940 only a fool, or a man blinded by rabid hate, would trust the safety of a small, weak, nation, to the good will and restraint of Adolf Hitler, once Hitler had that nation in his power.
Hitler talked nice to DeValera, but the Nazi plans to subdue the Irish Republic -- once england surrenders -- were so far along by then that they had even calculated how many tons of shipping would be required to transport the Irish political class, and all Irish Jews, to the concentration camps on the continent.