There is a new class of buyer that sprung up when sellers could no longer leave negative feedback - the buyer that leaves 100% negative feedback to cause disruption. A seller can also open a new account and buy a large number of items from compeating sellers and then leave a large number of negative feedbacks to damage the reputation of competitors. We now have to scan for buyers that leave a large number and 100% negative feedback for other sellers that we believe to be very honest. Then we block these buyers from bidding on our items. Then, sure enough we will often get a profanity laced e-mail from them wondering why they can't bid on our items.
Why should they have to? Where they driven to this because sellers have a no refund policy? Since the buyer can't examine the item before purchase then the seller must have a no questions asked return policy. If they don't, even if that fact is clearly advertised, then they open themselves up to problems. Have a return policy and this won't happen.
As an honest buyer, I don't want to be held hostage for my feedback. What if I genuinly need to leave less than positive feedback? Then I get trashed even though I fulfilled all of my responsibility by having payed. The seller wants to get even. That isn't right. As for those scammers you mentioned, I think that falls under the heading of petty crime rather than a legitimate buyer/seller relatioship.
Your points have some validity, but I think that on balance this policy is right.