You are just flat out ignoring the possibility that demand will increase dramatically at some point in the future. Also, halving 2016.
Let's try to gauge transactional demand as best we can.
Even if we do 640,000 transactions per day which is the limit for the 1mb block, at a price of $1200 miners would be getting paid $7 per transfer for security.
Is that really cheap to you?
Also why would demand increase substantially in the future. Obtaining a bitcoin is very expensive once you factor in commissions and slippage. It can cost even up to 10%. As an example the bitcoin ATM's charge 5-7% on top of slippage.
Bitcoin's biggest transactional demand comes from areas where fiat transfers are prohibited or too difficult. That electronic store for example that takes BTC only said a huge portion of their sales are coming from high risk credit card countries like Pakistan etc. Like it or not, cybercrime and unlicensed gambling account for the vast majority of transactional demand. There simply is no incentive for an average user to give up consumer protection, palm prints, ID's to buy bitcoins at huge markups and spend them at Overstock. All these so called bitcoin adopting merchants are just exit conduits for miners and large holders, and guess what? They all settle in fiat.
