I don't think Locke is evil, he is acting in what he thinks is the best interest of everyone. He could be deluded, but he thinks it is the "right" action.
His leg problem cleared up because he was losing the use of them because he was losing faith in "the Island" once he was forced to face Boone's demise (and realized that was his vision in the first place) his faith returned and he was able to use the legs again. If he doesn't think the island has fixed his legs, then it hasn't.
Of course if Locke grabs the gun and shoots Jack next week then I'll agree he is probably evil. The great thing about the show is
That Could Happen
I stand corrected, you are as vapid as they say.