I bet Katniss feels really stupid for volunteering

Nah. If she hadn't volunteered she would have watched her sister die on TV and gone back to a life of poverty and hopelessness, made worse by the fact that she'd spend the rest of her life hating herself for not having the guts to step up and volunteer when she had the chance.

When there are no good options and things are guaranteed to go pear-shaped no matter what you do, sometimes the only good thing in the world is knowing that at least you *tried* to make things better.

Not at all. Because of that one act it led to her taking down the who establishment and ending the games. Plus her and Peeta ended up together. Plus I agree with the other poster that she would have had a hard time living with herself that she stood by and let them take her sister. There are always casualties along the way, however, good had finally prevailed.

The fact that her attempt to save her sister fails is a tragic irony, but it in no way negates Katniss' heroism and leadership
in the revolution.

Disagree. That one pivotal moment resulted in a lot of positive things happening.