As someone who isn't a Muslim but can kind of sympathize with there being virgins or sexual relationships in the hereafter or next life, I think some people actually make fun of Islam for teaching the concept that there is enjoyment of sex in Heaven. I think it is nonsense and kind of hypocritical because God created Adam and Eve and created human sexuality and the body. And he said all of that was very good. There are also people on this planet who are unhappily single and long for the kind of intimate physical and spiritual bond that couples enjoy, and like it or not also have sexual fantasies that remain unfulfilled. But because we live in a fallen and unfair world, these people can't obtain it for one reason or another, especially in the "proper" God-designed way.
Well, the reason probably covers anything from general Islamophobia to genuine criticism of the idea that a person could be offered as a prize.
Muslim scholars themselves are of many diverse opinions on the subject--the Qur'an itself never mentions "72 virgins", but speaks several times of "companions"--but the interpretation of this is diverse. From viewing them as women, as men and women, as righteous people of this age, to a special new creation by God in Paradise; from literal to completely allegorical. Hadith and commentaries have, over the history of Islam, provided a highly diverse set of ideas and interpretations.
So there really isn't a "Muslim belief in 72 virgins", as that seems to just one possible understanding, though perhaps one that, historically, was popular at least in certain schools of Muslim thought.
Hence, Islamophobia can play a role here--assigning all Muslims as believing that men will get 72 virgin women as prizes when that isn't the case, as a way to simply ridicule all Muslims.
And also genuine criticism, where those interpretations exist which have viewed it this way; but without attempting to lump all Muslims together.
I do consider the idea of people being regarded as prizes to be extremely problematic. But since it's not a universally held Muslim belief it's not something I've ever really focused on in inter-religious conversations with practicing Muslims.
-CryptoLutheran