Except that the point of the parent post was that people would always hoard bitcoins and never spend them because the value would always rise.
If you don't expect it to always rise, then you don't have the issue (not that it would necessarily be one) in the first place.
The conclusion that Bitcoin will only get more valuable as time goes on depends on the assumption that it will acheive and then durably retain a certain degree of importance as a currency.
The people that are pointing to the problems associated with that are not arguing that they believe that will occur, they are making an argument about either why it shouldn't occur or why they believe it will not occur (and, often, both simultaneously.)