You need a counter balance to do that thinking. If you just watch and think about what you watched, then you don't really have an alternative perspective, That is why hobbies or something that gets you into more hands on experience in life is important.<quoted text>
It depends. Watching TV too much rots the brain. Perhaps watching TV then taking breaks to think about what you have watched might be more stimulating and more healthy.
It takes time to digest things you "learn".
Being dumb and letting others pour things into your head is dumb. But it is something people do.