I don't think that's true but he couldn't understand Buffy's conscience if he didn't possess one himself and Buffy's conscience is an essential part of her. An essay in 'Why Buffy matters' puts it better than I could 'he doesn't yet know all of her, he doesn't even know all of himself'.As I said in an earlier post, having no conscience or moral guide would actually make it easier for Spike to love (or at least feel the emotion that he identified with that word) because he would have no inhibitions about who, or, for that matter, what, he chose to love. Race, age, gender, even species, wouldn't matter in the least, because he wouldn't have any restraints as to what was considered right or wrong. Spike could just as easily claimed to love a male water buffalo as Buffy, and he wouldn't see anythig wrong with the idea at all. If it feels good, do it. Spike apparently was unique, however, in that, unlike his mother when she was turned, he drew the line at incest.
Maybe what soulless Spike called "love" was actually just lust, but for him apparently the two were virtually one and the same.