Not at all. I know it's confusing, but bear with me, or try it out if you have a freewheel lying around like I do.

Suppose you put same size chainrings on both sides, a 16T freewheel on the right, and a 20T on the left side. When you pedal forwad, crank turns right freewheel turns wheel. Simultaneously, the left crank's chainwheel is turning, trying to feed exactly the same amount of chain through the freewheel as the right side one. As this cog is larger, it will be forced to turn slower than the right side one. While both chains travel 80 links, the right freewheel will have to turn 5 rotations, the left side one 4 rotations.
Now, given the structure of the freewheel, when it's mounted on the left side, it can turn forwards as fast as the wheel, or faster, but not slower. When the wheel is stationary, the left-side-mounted freewheel can turn freely forwards, but not backwards. (<--Backwards, it drives the wheel, obviously).
So, you couldn't go forward at all with this setup.


Conversely, if you put the larger freewheel on the right side, the left, smaller freewheel will be turning faster than the right side one when you go forwards, freewheeling away happily, and you can ride the damn thing. (This bike obviously couldn't be ridden backwards.) What I don't know for sure is what happens if you try to backpedal. Supposedly, you get a larger gear ratio (not much fun at all, BTW), with the right cog freewheeling... This, though impractical, should work, shouldn't it? Skidding definitely would be ok as long as you can skid the larger gear.



Now, what if you use a trials setup: fixed cogs, freewheels at the cranks? I'm lazy to think it over.

But...

Somebody, please build a frankenbike with two different-sized freewheels and cogs. Say, 44/16 and 55/20