(I don't think that's how it actually works, but it's the sort of counter-claim you hear advanced. Don't ask me to defend it; I can play devil's advocate pretty well, but to do so I need to be able to see the devil's point of view, and in this case I can't - where I live, the claim's often made about rats, but my observation has been that Baltimore rats don't give a good goddamn whether a yard is mowed or not.)
If I want to sell my house, the value is somewhat diminished by your presence. Ergo, peer pressure and government ordinance arise to settle the dispute.
Otoh, if you want to live somewhere without those things, get a home in the country where you can get more acres for your buck.
Normally, I would agree that individuals should be able to do as they please with their property; I'm typically a libertarian fellow. In this case, though, it's fairly obvious that "proper maintenance" is established to prevent harm to others, and that harm can be objectively measured.
With all of that said, I definitely wouldn't live anywhere with a housing association; there are limits to the above argument that I find they frequently cross.
> In this case
S/he is living in the country.
Sure, but that's the easy road to never settling the burnt feelings and the idea that your neighbor is "getting away with lawn murder".
Basing the standard in eco-science may mean a standard that everyone hates, but it's firmer ground that can be argued rationally.