In a way, that's true. Drinking a lot of juice, or soft drinks, is not ideal, and when I see an overweight person drinking straight from a large juice bottle, that reaffirms my belief. It would be socially unacceptable to judge this behavior as being caused by cognitive deficits, but you could argue that such people are acting against their own interests (which is a very human thing to do, we're not machines).

The case of watching a lot of TV is a bit different though because it's about attention. Time is limited and it makes a difference whether I do something intellectually stimulating or not. If I spend 8 hours per day creating things, writing software, learning languages, etc., that is going to develop my brain in a different way than 8 hours of watching TV does.

Now to the point about the bad look: even if the study could not prove a causal relationship, why would you even risk it? There is little to gain from watching lots of TV and you'll end up healthier and happier by prioritizing other things.