Ron Purewal's super helpful reply on
MGMAT forum:
we're looking to WEAKEN THE CONCLUSION.
the CONCLUSION is
"the plan has promise of achieving the twin goals of giving the former hunters a good income and helping ensure the manatees’ survival"
therefore, we can WEAKEN THE CONCLUSION by showing either
* that the plan will NOT give the hunters a good income, or
* that the plan will act to ENDANGER the manatees' survival.
--
the correct answer should be (e).
if the hunters would have to "would have to use far larger boats and make many more trips into the manatees’ fragile habitat than they currently do", then the manatees' survival is being placed at increased risk. note especially the pointed use of the adjective "fragile".
(a) is irrelevant.
it doesn't matter that MANY tourists are uninterested and/or unwilling to pay for the tours, since the passage has already guaranteed us that "tourist interest is high".
MANY just means that we can find a bunch of tourists who aren't interested. this doesn't, at all, weaken the conclusion that tourist interest is high.
analogy:
if i determine that, in some area, local interest in eating cheeseburgers is high, then i should probably open a burger joint (if there isn't already one open) in that area. if i find "many" people in the area that don't eat cheeseburgers, that doesn't impact my existing statement that local interest in eating the burgers is high - again, we don't need everyone to be on board.