The objection is you're committing fraud. You're soliciting 'donations' for a third party (everyone committing to a project) without their consent. Unbeknownst to the donaters you're then keeping these 'donations' because the third-party has no interest in taking them. This is pretty shaky ground to be on, and it only takes one person to decide to take legal action against you.
They should simply state and then execute that refused donations will be sent to other projects or returned. I don't think this is that big of a problem.