What's the difference between Tosafos' second kashya on Rashi vs. his third kashya?

We understood that Tosafos' second kashya is that ka'asher zamam is a chidush, giving intent greater status than successful implementation of the din, only in situations which have a psak din and a bitzu'a of the din, ie death penalty; there, we can say ka'asher zamam and not ka'asher asa. But in Ben Gerusha,etc, there is no distinction between psak din and implementation; because there is no implementation. this is what we said Tosafos meant when he said there's no mikor sheyitchalel hazama; without a pasuk, logic dictates that the zomimim shouldn't be mitchalel for hazama alone. But then Tosafos' next question is that the kal vichomer doesn't work in the case of sokel because it would be mivatel Toras Edim Zomimim, which is not the case by Chilul. Isn't this essentially the same kashya? The reason the kal vichomer wouldn't be mivatel the din of edim zomimim by Chilul is that there is no pasuk there to preclude paturing the edim for intent only.

R. Meir, Jerusalem