Honestly I like advertising in general, but Targeted ads are the problem. Billboards are the least targeted ad.
Bizarre.
Trash is trash whether it's a piece of paper on the ground or blown up to billboard size.
In your perfect billboard free world, would you also ban signs outside of a business saying what is on sale? what about signs outside a private residence?
What kinds of property would be allowed to display what kinds of sign?
I could see telling government agencies they cant rent billboard space out on the side of the road, but if someone puts a billboard on their roof or the edge of their property I think it would be gross to stop them.