Ads can have positive effects for society too. Say your hotel is empty and you advertise half price rooms - everyone one wins compared with that being banned.
It's not "effectively" an ad for anything, it's a discussion forum. The fact that it also offers some publicity to YC's business is an additional aspect, but not the main one.
Banning all color in ads, all images/videos in ads, all ads in public (busses, billboards, etc), music in ads. Simply black and white text information (which is what YC adheres to).
Good point. So where do we draw the line between good advertising (i.e. new products, new movie trailers) and bad advertising (i.e. “beauty” product manipulations, sugary drink commercials)?