If it is only free in order to inconvenience competitors in a way that will eventually reduce choice, either giving you undue control of a market or being done with a view to charge later when people have no choice as the competition is broken, or both - that is when free becomes an anti-consumer matter.

It is an issue that you sometimes need to think long term to notice. If you wait for it to be an immediate problem, it is often too late to easily do anything about it.

Your food example is exactly what people feared would happen with IE, and what actually did happen for a long time despite the anti-trust case: client side developments stalled because IE was such a large part of the market and it did not implement anything new because there was no reason for them to. There was not sufficient competition to make it inconvenient for the incumbent to stagnate, so the whole area stagnated somewhat until Chrome came along and stirred things up a bit. MS was in control due to an effective monopoly, the consumer suffered.

Not 100% apples-to-apples, but I imagine you've heard cases of "big players" in various industries lowering their prices to the point of selling at a loss, which drives out the small players (Amazon, Wal-Mart come to mind). In the end, only the big player is left, and they are now free to raise prices.

I think it's reasonable to see that initial low-prices (could even be free) period of behavior as anti-competitive, since it may ultimately stifle competition in the long term.