The reason many people hold the harmonica with their left hand is because they keep the low notes of the harmonica (holes, 1,2,3) on the left hand side, and high notes on the right side.
Since the low notes are used for bending and vibrato a lot, holding the harmonica with the left hand allows a player to create a more airtight seal around the lower holes and their lips. Similarly, people who hold the harmonica upside down (low notes on right side) hold the harmonica with their right hand.
If you feel comfortable holding the harp with your right hand, and find the left-handed grip unnatural, just stick to whatever feels natural to you.
However, if you keep the low notes of your harmonica on the left side, and use a right-handed grip, I do think it would be a little difficult to get deep "wah wah" sounds on the low notes.
More info can be found here:
My Lessons go into more detail: