This already happens to some extent but it is a balance between allowing content without requiring approval and stopping inappropriate content. User-created streams can set an option to require moderator approval for all content.
i have an idea to make imgflip more safe
in a nutshell, when a user creates an image, sitemods need to approve the image first before submitting it in a stream. this would make it so imgflip users wouldnt have to look at jeffrey, corn, ect. but it would make sitemods jobs harder because of all the extra images. to solve that, you could recruit more sitemods. and when approved images are submitted in a sitemod owned stream, it gets auto approved since the sitemods saw it already.