I expect there are plenty of people who would take exception to Ellen's tactic, here, her attempts to educate Eric from the perspective of "here's another, better, more effective way to attract sexual partners". No doubt, they might prefer it if Ellen lectured him on basic feminism and respect, ideally while continuing to kneel on his sacrum - and certainly, he richly deserves it.
Of course, she's not doing that for the same reason that she paid for his frozen yogurt, rather than insisting he pay for hers - people are always more inclined to listen when you phrase your message in a way that furthers their self-interest. If Ellen's dialogue over the past five strips had been nothing more than a list of Eric's wrongdoings and wrongthinkings and a standard of behaviour she'd have preferred he follow, he might have hastily agreed with everything she said in order to get through the conversation as quickly as possible, then gone home retaining nothing more than "you're bad". Most likely, he would have resented her for making him feel this way, and, by extension, become bitter at feminism itself.
Everyone on this planet is evil/ignorant/insensitive about something. Pride yourself on not being sexist or homophobic? You probably don't realize how racist you are. Pride yourself on never discriminating based on race or creed? You're probably ageist or ableist. And so on. Everyone deserves a harsh lecture about something, but there's a big difference between what we deserve and what effects positive change in the world.