If all we're left with is walmart and they raise prices then that opens the door to competition. They only dominate because they offer low prices and large selection at locations that are convenient.
This sounds nice, but in reality, it isn't true. The way corporations are set up nowadays is that they own every aspect of the process. Wal Mart doesn't buy furniture from Martha Stewart then resell it, like a small business would. They create the Martha Stewart furniture and then sell it.
Wal Mart doesn't have Wal Mart brand food cheaper because they want poor people to be able to enjoy knock off fruity pebbles. They have knock of fruity pebbles because if they can get everyone to switch to Wal Mart fruity pebbles, they can buy out/force fruity pebbles out of business.
If all we are left with is Wal Mart, then all we will be left with is Wal Mart.
For example, there is a dental company called Aspen Dental. They have offices all across the country. They have their own in house dental labs. When they open a new office, they do free exams and xrays, and fully plan on not turning a profit for 3-5 years. Their hope is to have their prices so low, that they force the competition out of the area, and when that happens they raise their prices.
When all that is left is Aspen dental, that will be all that is left. The reason why is because nobody will be able to start up a dental practice for free. Aspen will just undercut the new office, lose money on that location until the competition is gone.
Wal Mart will do the same. As will Comcast, Disney, AT&T, etc.
This idea that there will always be a place for competition isn't reality. It sounds really nice. I spouted that off for years, but in reality, it won't happen that way.