While I'd normally endorse a cache placer's right to break the law if they really wanted to, it's the whole activity of geocaching that would suffer if this infringing placement was discovered and became an excuse for even more stringent measures and derailing any future discussions about lifting bans, etc.
In much the same way as unpublished vacation caches or archived unmaintained caches on gc.com probably remain as litter, at least there's a message that ignoring the rules won't be rewarded with an active cache, making it more likely that a placer will check before going to the effort and expense of placing the box.Banning geocaching in these areas will not always result in less "litter".