Also have been hearing this not too seldom. Notice that, again, this is not a newbie member:
Just a blatant misunderstanding of the mechanism of difficulty re-targeting.
If bitcoin was worth 2 dollars a coin it will quickly cease to exist. At 2 dollars a coin it is not only NOT rpofitable to mine, it is actually going to cost people money to mine. Bitcoin needs miners to process transactions, without miners the blockchain freezes and no confirmations are made on your transactions, So at 2 dollars a BTC no one would want to mine much less be able to afford to mine.
Just a blatant misunderstanding of the mechanism of difficulty re-targeting.