I also watched Goldwater's slide into 'PW' territory. I would agree that a combination of declining mental abilities and a 'boost' to the libido by a young woman combined to push him in to supporting the killing of babies. Just listent to Granny 'D' and the sudden on-rush of tolerance by aging types - somehow the 'tolerance' never includes embracing moral standards or personal responsibility.
That liberal view probably led him to other liberal views, as those holding that homosexuality was errant and wrong were the Conservatives. Disaffection with the Republican take on homosexuality probably tainted his opinion or judgement on many other Republican views.