Without their user's content the platform would not exist. Just because they host the content and apply an effect to a photo taken by you, does not mean they have the right to sell it without paying the person who created the photo in the first place. Therefore I propose that Instagram come up with a payment system that decently compensates the users whose photo is sold.
If Instagram does not agree with this logic, then they will have to deal with the consequences i.e. a mass exodus from the platform to another photo sharing service like Twitter.