Abortion was not an issue when Goldwater ran for President. He may have moved left on social issues in his declining years, but people were not factoring those issues into whether to vote for him in 1964.
Goldwater was always more of an Arizona libertarian. He was very typical of the people who were born and raised here. It was mostly "go away and leave me alone" and "America should be strong so it WILL be left alone" His stance on abortion was because of those libertarian leanings. He might not have approved of it, but figured it was none of his business and for sure wasn't the government's business.