The resources that are spent on cosmetic purchases could instead have been spent elsewhere, possibly providing a better overall gameplay experience.
I don't think anyone is arguing that freemium games can't be fun or that some microtransaction models are more player-beneficial than others. But, like with any feature, if you include microtransactions than some other aspect received less attention (assuming a fixed budget, which I realize is also a consideration as game X might never have been made without the freemium component to propel the business decision).
Edit: Also, as others have said here, most freemium developers focus on extracting revenue from the "whales," not the players who play for free or pay little.
I don't think anyone is arguing that freemium games can't be fun or that some microtransaction models are more player-beneficial than others. But, like with any feature, if you include microtransactions than some other aspect received less attention (assuming a fixed budget, which I realize is also a consideration as game X might never have been made without the freemium component to propel the business decision).
Edit: Also, as others have said here, most freemium developers focus on extracting revenue from the "whales," not the players who play for free or pay little.