Here's the way I see it. From what we've read in the Xehanort reports, MX had very good intentions, as well as some intelligent ideas. He wanted to maintain a balance between darkness and light, and resolved to delve into darkness in order to achieve that balance.
However, somewhere along the line, I think MX was corrupted by darkness. He went to the extent of killing his former friend (Eraqus) and stealing the body of possibly the most powerful Keyblade wielder yet seen (Terra).
There is a chance that Xehanort still wishes to achieve this goal. Perhaps that he, like Xemnas, truly wanted "a brand new world"