They are right in the effect. However, you never see anyone take it to the next step. Do we NEED to market to be THAT liquid?
We can't really know the answer to this. The applications that would benefit from instant liquidity haven't been developed because instant liquidity has not been available.
Maybe there are some true killer applications for this that just need a few more years of HFT-provided instant liquidity for someone get around to inventing, and once they do, we'll all wonder how people could even pay their bills under the old system let alone live their lives to the full.