I would agree with ed that free enterprise and competition can be a healthy thing and that instability caused by competition usually evens out. But one of the problems is that the trend in capitalistic societies is for companies to gobble each other up and ultimately, we end up with monopolies that control all the prices, with no other motive than profit... that is not usually a good thing for the consumer. The telephone service was privatized in Mexico some years ago with disastrous results. It was set up as a monopoly (TelMex) with disastrous results. Mexico is now the most expensive country in the world from which to make a phone call, either local, long distance or international.
I would agree with bloc that privatization is good for a lot of things, but not for education or health care. Although I would reverse his final point and say that education is debatable, but not health care. Private schools can and do do a good job of educating. The problem is that not everyone can afford to send their kids to private schools, so a free education needs to be available to everyone. With profit as the primary motive for health care, we can be pretty sure that our health care professionals are not going to be making the best decisions for us... even if they want to.