I'm not convinced that sales will be hurt that badly.
Again, no one I know, myself included, is happy with the stance that Target is taking. I'm just not convinced that they had any viable alternative.
By extension if, as a for-profit business, they didn't have a viable alternative, a boycott is not going to be very effective.
I'm also not sure what the alternative would be: Letters to Target management, letters to the paper on behalf of Salvation Army, letters to the pro-gay groups (yeah, right), letters to your representatives demanding tort reform... I don't know if any of these would be effective either.
You do what is right and damn the perverts.