Baby aces, please read this as I am seeing these terms swapped out and misused a lot lately.
Sex-negative, sex-neutral, sex-positive. These words are about your cultural perception of sex. What value do you assign to sex in a general sense? Is it something that is dirtybadwrong and should never be talked about or is it a potentially positive experience between two consenting adults? Should we teach kids comprehensive sex ed? What are your attitudes about kink?
Sex-repulsed/ sex-averse, sex-indifferent, sex-favorable. These words are about your personal perception of sex. Does thinking of yourself actually having sex make you feel completely grossed out or just give you an overwhelming sense of "meh"? Would you enjoy it or be willing to do it under certain circumstances or is it just icky and off the table forever?
You can be sex-repulsed and still be sex-positive. Most aces I know are sex-positive!
I've seen the aphobia rising again on tumblr and, obviously, fuck those people forever. Thinking about them is not worth the time or effort. But I do worry this growing trend I see of aces proudly proclaiming they are sex-negative when they probably mean sex-repulsed is contributing to confusion in people who would otherwise be allies. Because that first set of words is common outside of the ace community. If you tell somebody who is active in queer and leftist spaces, but knows next to nothing about asexuality, that you're "sex-negative," they are probably going to jump to very wrong and unfavorable conclusions because sex-negative attitudes are inherently anti-queer.
Edit: I put the link to AVEN's section on these terms in the replies.