The problem on most forums is that people say "don't feed" while continue feeding (not necessarily the same people are engaged in both parts). I believe that the not feeding policy works because (1) I don't remember seeing a really obnoxious trollish exchange not feeded by non-trolls (itself a weak argument, since I don't frequent troll habitats often), (2) it corresponds to my proto-model of troll motivation, which is seeking attention (also a weak argument, I don't really understand trolls) and (3) the trolls need something to react to, and the responses to their debate contributions provide more material and thus opportunities (this is a bit stronger argument, it seems almost self-evident).

The continued simultaneous existence of trolls and the no-feeding policy doesn't say much and is well compatible with the policy being effective. Note that:

• The claim isn't that non-feeding is capable of eliminating all trolls in any situation, but only that it reduces the negative effects of trolling.
• The non-feeding policy, although well known, isn't universally applied, and trolls can easily thrive on places where the local debaters lack discipline and engage them.
• To show that the policy doesn't work you should compare two forums which have (approximately) the same topic, the same moderation rules and comparable audience and differ only in the troll-feeding attitude.

To further support your claim it would be helpful if you provided an example of a troll-disrupted discussion where actually nobody was feeding the troll.