There are loads of arguments that point against using closed guard on the street:
1. Stuff on the ground: Guard may be fun to pull on your cushy dojo mats, or even a hardwood gym floor, but try that shit on a real street, with concrete, bumps, broken glass and garbage lying around, and everything looks a little different.
2. Buddies: Its pretty rare that criminals operate alone, and if they aren't and you pull guard, you just signed your own death sentence, and believe me it will NOT be quick and painless. If its a street fight due to bullying, or someone acting like a jackass, odds are, they still have some kind of buddy around to stomp on you. I almost never see people that would normally walk around in an agressive enough manner for you to get into a fight with them that don't have at least one buddy around.
3. Weapons: If the guy pulls a knife on you and you're on the ground, you're in a LOT more trouble than if you're standing. You have no real chance to get away now unless you defeat him in some manner (breaking something significant or choking him out). Someone attacking you with a knife while you're grappling with them will almost surely result in your death, (And then you'll never know if Chuck actually ever stood a chance against Fedor
(I doubt it))
IMHO you want to keep any street fight standing up if possible. Of course you want to know how to grapple because: a) Its sooooo fun, b) Its useful in "schoolyard" type fights, and c) if you ever do end up on the ground you at least want to know what to do.
Punching, kicking, and Throws are your friend on the street. (Especially throws for that matter, try a real seio-nage on someone on asphalt, and around 90% of the time, they will be knocked the **** out or so winded and injured they wont do shit all anymore for the next three weeks!)