adverts fascinate me as a study of societyThats a nice perspective, I might try that. The science of advertising is also interesting - these marketers spent squillions of research dollars on figuring out the most effective technique to transfer an idea/emotion/brand (essentially a meme) to your brain. Those techniques are also applicable to giving a presentation for work and public speaking. I've noticed the most successful people in the workplace are those who can 'sell' their ideas to their colleagues and managers.
But are TV adverts really more "mentally polluting" than a 80s song or a limerick you picked up at a schoolyard?
For the most case I think you're right. There is a subset of more evil adverts which attempt to play on insecurities (body image, gender roles/responsibilities, medical fearmonging). But most advertising is just...transient noise. Never attribute to malice what can be explained by banality.
I have a pet theory that our brains will retain a certain amount of useless 'mental pollution' regardless of what information streams are being thrown at it. Not because we need those little nuggets of useless information, but because they are implicit to the formation and recall of other 'useful' memories and emotions. Memory is a multi-sensory thing, regardless of what part of the memory is 'useful'.
Music is a special case, its ability to trigger episodic memories is very strong[1]. I like to think of it in computer science terms as a hash table[2]. If you spend enough time doing a certain thing whilst listening to the same music, the event is stored against the hash (music). Then in the future, listening to this music will trigger a very strong memory of that time in your life.
I spent many hours as a teenager listening to music whilst playing video games. Now if I listen to these albums, the memories instantly 'come flooding back' as the saying goes.
[1]I believe olfactory triggers are stronger than auditory triggers. Perhaps smell-o-vision advertising is the next big thing.
[2] Not a great analogy - the linking and recall is really bidirectional.