I can easily look either side of the sign and see the same thing I would see where the sign is. I genuinely don't see the downside.
We live in a democracy and it's up to a majority to decide what to do with the public commons. It is telling, to me, that no state that has banned billboards (Alaska, Hawaii, Vermont, Maine) has any serious political movement from any part of the spectrum to reverse the bans.
Why should one profit-seeking entity get to put a billboard in the middle of everyone's scenic view without paying everyone?
And if one billboard can be put there, what's to stop there being ten, or a thousand, and then there's no more view?
A lot of problems in the world are due to profits being made at the expense of the commons. This happens with everything from resource extraction and pollution of the environment, to telemarketing which aggravates most people, to outrage driven media and social networks polluting peoples minds.