While I think our behavior and actions towards Native Americans was horrible and disgraceful, I believe thanksgiving (at least for me) allows me to step back and appreciate my family and be grateful for what I have. I also donate food and participate in food drives, and really enjoy it, and know many others who do also.
While I think our past actions were unacceptable (and perhaps even the attitude towards Native Americans today), I can't change time, nor can I change the actions of everyone.
I think our actions should be remembered, as to not be repeated (as goes slavery... animal cruelty?), but I think the holiday today has evolved into something different, just as with Christmas. Many people celebrate Christmas (me, my boyfriend, best friend), however we are not religious. I think that for many (note: not all) certain holidays have become time off to spend with family, give gifts, and perhaps even give to those less fortunate, and almost have lost original intentions.
I think perhaps having a day of remorse/remembrance or a month dedicated to the past might be better, than turning what is now usually a happy holiday (aside from all the pigs and turkeys that are slaughtered) into a day of sadness as it wouldn't accomplish anything.
The world's past history is filled with unjustness, brutality, and cruelness. I think without breaks every once in a while, many people would be much more miserable, leading to an unhappier world.
But that is just my take on it.