That's the argument for sea-based launch platforms, and its a pretty good one. This floating platform would probably have to be launched from a sea-based platform, and then you would have to chase it back down. Altitude and attitude control would be a real problem.
Not if the weather is bad when you're getting ready to launch the platform. The weather conditions might have to be even more stringent for a platform that is held aloft by 4 gigantic balloons.
This might be true, although I wonder if the largest forces at work on a rocket are really aerodynamic or just acceleration in general.
Edit- This depends on the speed of the rocket and when it is during the flight. Most rockets experience Max-Q due to aero drag at about 50,000ft or so.
How the heck are you going to steer the launch platform around in any kind of surface winds?? Just release it and hope it stays level?
I think the real problem is just that rockets capable of reaching orbit with an appreciable payload are BIG, and can't really be carried by an aircraft (especially not in a horizontal orientation).