Speaking on the gay male side, the convoluted answer is:

-- Same-sex friends-with-benefits can get messy

-- But same-sex friends-with-benefits can also go smoothly if both parties are clear about what they want/expect (and maintain the friendship)

-- There are some things (especially sexual topics) that gay men can talk about more easily with other gay men (or bisexual men) than with straight/gay/bi women or straight men