They kinda bring the pride of countries together. I like ads for Hunts, for cars, for Malboro (even though I don't smoke). I think ads are really cool. I know some people have complains about them, which I don't mind, but personally, for me, I think ads are awesome on highways.
I don't really care what the ad is, if it's causing people to look away from the road, it's dangerous. Reading a speed limit or exit sign is one thing, it only takes a fraction of a second, and you are unlikely to need to read it again the next time you take the route. But if you see an amazing 70% off deal on a giant billboard and you're wondering what the catch is, because you KNOW you see that asterisk, you're going to look a little harder. You take your eyes away from the road long enough to read that sign, positioned farther away than street signs (which are purposefully lined up along or in the center of the road so you can read them without crashing), and BAM! You just hit me in my tiny honda civic with no airbags (because it's ancient), with my eight month old infant son in the tiny tiny backseat.
It's just not worth it. We get plenty of really cool, funny, and interesting advertising on television, online, even as we walk through a store, I just don't see why advertising on a highway is necessary when the benefits are few and the possible consequences so dire.