I only mention this because I have the same rhetorical tendency and people always somehow seem to think I'm equating the two: it's not a statement that milk equals rape. It's highlighting (with a stark example, arguably an unnecessary one) that a person deriving pleasure from an act doesn't make the act immediately good (I dunno, stealing candy from a baby? For a less "vivid" counter example; I admit, I tend to use super obviously morally bad counter examples too, thinking it'll make things more overly clear, and, instead, causing someone to think I think they're the same thing rather than just operating under the same principle, of differing degrees).
(all that said, their argument doesn't hold water, to begin with, as it's not cruel or painful to the cow unless under factory farming and cows have no sense of ownership and don't feel like their property is being "stolen"; a meal isn't a proper meal if dairy isn't involved, as far as I'm concerned)