I think that advertising is on dubious grounds when it exists as a substitute for payment (dubious because of the extremely low payout compared to the inconvenience / damage caused).
In public spaces, on transport systems and so on, things that can't be avoided and are either already paid for or aren't even being used (e.g. walking past an ad on the pavement which pays for nothing other than the land it sits on) it's completely inexcusable.
We're trying to encourage people to use public transport.
We need to do _everything we can_ to make it a better environment, more comfortable, more homely, etc.
Knocking out advertising would be an easy win. (Killing off the OTT announcements would be another one... but I digress...)