[iand]

People aren't backing out, they are reducing their pledge. Do same anti-trolling measures deal with that?

[_delirium]

Also not allowed. From the ToS (https://www.kickstarter.com/terms-of-use):

Backers may increase, decrease, or cancel their pledge at any time during the fundraising campaign, except that they may not cancel or reduce their pledge if the campaign is in its final 24 hours and the cancellation or reduction would drop the campaign below its goal.