I don't think it's the amount but rather the context given the character development. If the character is always ecchi then it makes more sense. If you have a random sex scene then it doesn't quite make sense. That's true whether it's anime or a romance novel. In fact anime is often compared to literature, as opposed to other visual media like television because of it's advanced character development. I've got no problem with tons of fan service but I agree it has to be paired with good writing. I don't find excessive amounts of Plot bad so much as badly written story and plot, now that's cringe. So in essence I would disagree with the assertion that everyone hates fanservice but add the caveat that randomly throwing in a sex scene does not automatically improve things on its own either.