Yes, people can do whatever they chose with their money.
Target should be able to do whatever they chose with their stores.
However, when people misrepresent what a business is actually doing by only telling one side of the story (target bans SA bell ringers) and ignoring the other side of the story (target still donates money and merchandise to the SA, Target had an exception solely for the SA for years, and target gave the SA a full years notice of their itnent), then it's morally dishonest of the people trying to make the case for the boycott.
If people were holding themselves to the same standard as target, they should be pilloried for not dropping some money in the SA kettle one time, even though they have made donations every time they passed a kettle for years. There is no attention paid to the reason for their decision, their past history with the SA, or their work with them (And many other charities) in the present.
The truth is that by christmas of 2005, there will still be no bell ringers at target, target will still be giving money and merchandise to the SA, and 90% to 95% of the people who promised to boycott target will have bought something from target or a related store at least once.
BTW, the stockholders won't like that 5-10% drop in sales do to a poor management decision.