The whole "no" argument comes from the need to protect ourselves...From ourselves. I don't need that done to me. If some idiot child wants to watch TV all day and not do anything then I say let him. (From a government standpoint not a parenting one.) He will not do well in school (or maybe he will) and that will be his choice. Whatever problems arise will be his fault. The "no" argument comes from a pseudo-communism, authoritarian ideology that limits our freedoms.
Outside of school, what you do is your own choice. Students work hard day to day in their classes and when they get home from school they need to relax and take their mind of things for awhile and if they want to watch TV for an hour or so they should be able to.
In order for students to retain the information they were taught in the classroom, it makes sense to sit down and get started on homework as soon as possible after getting home from school. This will also keep them from forgetting about assignments, and make them prepared for the next day of classes. After this is done, there will hopefully be time in the evening for whatever they wish to do in their spare time, including watching television.