Why might a compact drivetrain be frowned upon?
While Machismo answers the question asked, the reason why there is that reaction is mainly a lack of understanding about how and why compact cranks exist. 

Obviously, you can look at it and say to give us better climbing (easy) gears. But what many people miss is the rear ratio changes.

The race standard for many years was 53/12. That is, the hardest gear, made up of the largest tooth count in the front, and the smallest in the back, was a 53 tooth front chain ring paired with a 12 tooth rear cog.

A few years back, Shimano started making an 11 tooth rear cog. It was originally intended for pro racers and time trialists. 

Somebody got out the calculator, and realized that with that 11 tooth rear cog now available, you could decrease the size of the front rings, and get the same gear ratio, or slightly faster. That decreased front ring size allowed better climbing ratios when paired with the large cogs on the cassette, but also maintained the high gear speed racers are used to. 

Someone riding a properly setup compact crank, actually is pushing a harder, faster gear than the 53/12 "standard". That said, if you pair a 53 with the 11 tooth, it will be faster yet, but not often do you find the legs to push that combo. 

I've included gear inch charts for both, so that you can see for yourself how it works out. If you are not aware, gear inches are a comparison to the effective diameter of a direct drive wheel, when gear advantage is accounted for.