At the Purim Seudah we are on a higher madregeh then at Neilah of Yom Kippur.

I went to a Shiur last night by Rebetzin Kalmonovitz last night  who said that at the Purim Seudah we are on a higher madregeh then at Neilah of Yom Kippur.  Hashem opens gates that are not open at any other time of the year.  Hashem forgives us for things that we did not do Teshuva for, and for things that we did intentionally, as long as we are filled with the Bitachon that everything that Hashem does is for the best (like in the story of Mordechai and Esther).  This is the reason for wanting to be in a state that we dont know the difference between Bless Mordechai and Curse Haman.  In the end, whatever happens is for our best, so even the seemingly bad is really a blessing.