I think Buffy HAD to look at the bigger picture in s7. They were at war, and war is not won by thinking of the small guys. Plus, I still think she had enough consideration for the potentials, but truth is she had to train them, she had to get them ready for what was to come. They weren't her friends, they were her army, and she had to draw that line. That doesn't make her a good leader, but it makes her what a leader has to be in times like that. Plus, Buffy offered those girls protection, so to me she was still taking care of them. Killing around 20 girls to save millions is a choice that was pretty simple for Buffy in my opinion. It's very sad for those girls, but unfortunately the bigger picture is more important.
PS. I'd be the first one to buy that t-shirt! It's awesome!