This is a terrible idea. Americans have been socialized to add ".com" to everything for the past fifteen years; consumers will never remember to drop the "m".
While I do like your last name, I have a hard time believing that "it's had an m for 15 years" is really the best argument against .co.
For example, does a .co domain inherently carry any security or SEO problem?
You missed the important part of my point, the part that came before the "15 years" part. If your business model involves teaching the whole world how to spell, you're doomed from the start.
it's a .co domain, so it has to abide by Colombian laws, say you start Google on a .co domain, then 10 years later there is a coup, and the new regime decides to take over your domain name