Sponsors who care about their content should put a warning message at the beginning of their movie trailers, like "approved for all tube audiences".
Some examples below, so that you can see what I mean.
Then let it be known that all other videos that are shown on public sites that do not have this warning are illegal and will be persecuted by law.
I haven't seen one single movie that had such a notice in place.
If all major sponsors adopted this habit, the tube sites could be controlled.