Could someone explain why anyone would be foolish enough to pay in bitcoins right now given its meteoric rise over the past few weeks?
Personally, given its volatility, it doesn't make much sense to me to hold much in Bitcoin outside of what you plan to spend relatively immediately. It could go up or down by 50% overnight - not a great store of value, either way.
There are reasons to not have all your money in bitcoins, therefore there are reasons to sell bitcoins (even if you just bought them specifically for that transaction (for the anonymity for example))
edit: I realised this sounds a bit snarky, but I'm honestly curious. Is buying with bitcoins really that different from not investing in bitcoins?
Why would I buy anything with my bitcoins if a week from now they're going to be work X% more? I'd just wait until then.
If you believe this, then surely you also believe you should invest 100% of your money in bitcoins?
If not, then you believe only X% of your money should be invested in bitcoins (to avoid the risk of losing everything in a collapse)
Therefore if you have >X% of your money in bitcoins, you should spend some.
A does not imply B.
If the currency deflates at 1% but you could invest at 2%, your mattress isn't the most sound investment strategy.