And again, I defy anyone to define "astroturfing" in a neutral way that everyone can agree on.
You're joking, right? As a Republican linux user, I haven't heard too many alternative definitions. Seems pretty clear to me...
Astroturfing: fake grass-roots activity. If you're trying to look like you're just a part of the "noisy populace" but you're being paid to maintain your position by the side you apparently agree with, then you're astroturfing.
That's one definition of astroturfing, but I'm sure that politicians may have another definition. Like, "any irritating deluge of calls from those pesky citizens" (who may really be concerned citizens being urged by an interest group that shares their interests to contact politicians on something they really, genuinely care about).
Be careful, because who is going to be applying the standard? It may seem clear to you, but laws often get applied far differently than their writers intended.
It's quite telling that groups across the spectrum, from the ACLU to various family advocacy groups, were against this portion of the bill. It quite literally puts a greater burden on organizations that want to keep the public educated about what their elected representatives may be doing.