4. Obviously 3% doesn't stop much trade, but 3% is worth 3%.
My point is that when Bitcoin has good (developed) escrow services, transactions will also have a cost.
Paying 3% still leaves the merchant with the risk of chargeback. No one else is even selling riskless payment to merchants online.
It's very likely that when both ways are widely available different situations will use different methods. Right now everything is being crammed into one setup - customer can yank back money and merchant has to collect info and still take risk.
Doesn't it seem a little bit odd that the best on offer for online payments is to hand over the exact info that someone would need to charge your card? It's a really bad system, but paying online is so valuable that we do it even though it costs billions paid to thieves.