The 6% is not the main problem, but it does have an effect. Not in the way you suggest though. The main problem is that the 6% reduces supply liquidity, which

The 6% is not the main problem, but it does have an effect. Not in the way you suggest though. The main problem is that the 6% reduces supply liquidity, which means there are less houses for sale than there would be otherwise. Owners know they cannot get back in easily at breakeven, due to the immediate 6% hit. That means when the market is hot, there is a tendency to hold on until it's not. This means the full extent of "affordability" is a more probable event. It doesn't work on the flip side when times are bad, because buyers have no such penalty. Whereas sellers are going to sell either because they believe prices will get worse, or are forced to due to finances.