It is not the supra-natural imposition on man, designed to show him a potential above himself to which he can climb. Purim is not a dignified holiday. It is not blessed with ritual. It is a day when you find the power to rejoice in God's goodness, in His charge to you, even though He is not demanding it. It is also a day of Jewish solidarity and equality.
Charity is of course a mitzva every day.
The mitzva to give alms on Purim is not a fulfillment merely of charity, but of the nature of Purim. You must search out the needy - and also share with your friends, although they are not needy. And, have a good time. Not telling us how to have a good time is a big risk for the halakha. There are, after all, so many ways to misuse human rejoicing.