Goldwater, and he would lose even worse today than he did in 1964. He would be attacked as a racist constantly, and his opposition to Social Security and Medicare would lose him many votes from olds and religious types, both key conservative constituencies.
How?
Goldwater was very critical of the religious right. Also, his support for abortion and gay rights wouldn't play well with that constituency.
What I meant is how his opposition to Social Security and Medicare would hurt him with religious voters, not his support for abortion and gay marriage.