Potentially unpopular opinion.
Hot Take but, Mileven fans aren't Eleven fans. They're people who see Mike as the average man, this figure of any man can see himself in him because he is any man. They dont like the pairing because they think she's supposed to be with him. Because he deserves to have the pretty, not-like-other-girls love interest. I just dont feel like they respect her as a person. Its always been about Eleven's relationship with Mike, and what she means too him. Even if Will wasn't in love with Mike, the Mileven relationship just doesn't feel fair. Im not saying all Mileven fans have this mindset, just that I dont get the feeling they like Eleven.