why do you think this? thats really not true unless A) you don't know how to drive stick properly or B) its a GTO

there are few cars in the quarter mile that are the same speed trans VS trans, and fewer that are measurably faster. gearboxes like the new Evo or VW DSG don't count.
there are plenty of reasons to not like automatics. they arguably break easier than a simpler manual transmission. fuel economy is better with a manual transmission. until very very recently you couldn't get a gear box with as many gears as a manual transmission. they're more expensive to replace or repair. they're one more option for the final price tag (as much as $1000 for some cars or more).
yeah, at the end of the day its nice on a commuter car to be able to slam it into D (which i'm told stands for "drive", even though there is substantially less "driving" involved) and putz around our congested hell holes without having to use your right arm for something other than picking a radio station or setting down your iced mocha latte comfortably into the cupholder. i'll agree to all that being the case from a comfort standpoint. but automatics - unless you're building one to rip down the 1/4 mile - have alot to be desired from a performance standpoint.