To answer, ask yourself if that guy in the cubicle next to you at work understands MMA and fighting in general. Do they get that when competitors only knew one thing, ground fighting or stand up, ground fighting proved dominant? What's more, do they realize how much knees, elbows, the clinch, and kicks come into play in a real fight? Sure, MMA's popularity is growing; and yes, there are more educated fans than ever before. That said, MMA is nowhere near the level of baseball or football yet. In other words, if Ray Mercer goes ahead and defeats Sylvia in a boxing match, a lot of rather uneducated people (fight game wise) are going to assume, being completely wrong, that a Mercer wins means that boxers are better true fighters than their MMA counterparts. They're going to start chanting that whole baddest man on the planet thing they used to say about Mike Tyson. And if you subscribe to the notion that MMA's rise in popularity has at least something to do with the fact that it's as real as it gets- that the true toughest man in the world might actually be an MMA fighter- then that's a bad thing for the sport.
Though the Mercer- Sylvia fight is a definite, there are more possibilities on the horizon. Anderson Silva, perhaps MMA's greatest fighter, wants to mix it up with Roy Jones in boxing. UFC President Dana White, of course, nixed the idea, as the organization has a contract with the UFC Middleweight Champion. Then Jones seemed up for an MMA fight with Silva. Again, White nixed the idea. The first decision made a heckuva lot of sense. Why put the face of MMA in a ring against one of the better boxers of all-time? Sure, Jones is on the downward end of a great career. That said, Silva would have to stifle years of using his knees, the clinch, and kicks. That would take conscious thought, which would certainly hurt him against a guy with Jones's speed. In the end, if this were a kickboxing match, Silva would have a good chance. In an MMA fight, if he fought the right fight, he would win hands down. But in a boxing match?
Boxing is Jones's sport, period. Now why White isn't up for an MMA match between Silva and Jones is a little more puzzling. It's also for a different article.
By the way, Nick Diaz has also called out Roy Jones. He's a pretty popular MMA target these days.
In the end, MMA and boxing are two vastly different sports. Boxers are the best there are when it comes to solely using their hands; it's just that simple. Could Sylvia catch Mercer and/or use his reach to defeat his opponent? Anything is possible, as Sylvia is a very hard stand up fighter to deal with and Mercer is old. But guess is that Mercer, with all of his years of boxing experience, is going to have a big time advantage here. If he wins, will it destroy MMA? Of course not; not even close. But such a loss won't help the sport by any means. Hopefully, the next time we hear about a high profile boxer taking on an MMA fighter it will be in the cage under MMA rules (not in the cage under boxing rules as will be the case at Adrenaline III).