Competition drives prices up.
With liberalisation the 'pie' get split up into to small chunks with each company trying to make a profit from each small piece.
More companies with smaller pieces means prices go up and stay up in order to make profit.
Prices rarely come down as each 'sector' closes ranks to keep prices artificially high. Look at energy prices for evidence of this. They all follow each other with regards to prices rises and more rarely price cut.
Examine utilities, comms, rail in fact almost any privatised industry and you'll see artificial price fixing/stabalising in operation.
RM is in trouble due to its would be profit being taken by DSA etc. What happens? Prices go up and services get butchered in order to maximise profits due to the pie being split.
Then the DSA companies go into partnership with RM (co-opetition anyone?) and close shop as it were, to keep prices high and the business model sustainable.
The only thing keeping Royal Mail alive now is the DSA companies. If RM were to fall, liberalisation would fail thus making the notion of the free market redundant. Something the big wigs wont allow to happen.