Theodore Hall says his motive is neither: "In 1997, Hall admitted that he felt strongly that an American monopoly on nuclear weapons was perilous and that atomic information should be shared between countries."

https://www.atomicheritage.org/profile/theodore-hall

There was a transition from early idealists imagining the wonder of the Soviet utopia which were quite prevalent into many of the more center-minded people realizing what was actually happening in the USSR souring on the whole idea in general. By the time the Manhattan Project was underway much of that transition was done.

There was another motivation which was strongly advocated by Oppenheimer and others to officially share nuclear secrets and bring the USSR to the table and establish controls in order to prevent secret competition and escalation. There were others who along those lines were motivated to use back channels to supply that same information for similar goals.

At least in the case of Klaus Fuchs, he was a member of a family active in communist politics in Germany before emigrating to the UK and then the US. Others are first generation born in the US, but at least in Seborer's case, the entire family seems to have been active in communist politics. The development of communist and socialist ideologies in the German, Austro-Hungarian and Russian empires prior to WW I provided a very fertile ground for recruiting among families who had fled repression in those regimes.