I think Instagram sell user photos is an invasion of privacy. the person may not want there photo used inappropriately. It allow a lot of people to do a lot of thing with your image for the right price. That is completely unacceptable. Not to mention the money being taken out of the users pockets that they could have sold the images to.
No, Instagram should not sell user photos to advertisers. As per the blog terms of service, Instagram sells users’ photos. Quite many people are shocked by the announcement. This is totally an acceptable. There is no business without a mutual agreement. It should be considered as theft and the blog should be accountable.
I think that if they do that, they are making a big mistake. It seems that it could also open them up to lawsuits, especially in cases regarding photos of children. That is a violation of people's privacy, the people who use their products and are therefore their customers. They should definitely rethink this.
Instagram should not sell user photos to advertisers. Although they are probably legally allowed to it would be morally wrong. People do not expect their personal photos to end up in an ad somewhere. It would also prevent a lot of people from using Instagram in the future if photos were sold to advertisers. Many customers would see it as a violation of trust and would cease using the service.