If we launch stuff from stations in orbit, the thrust used to launch the rocket will also launch the station backwards in the opposite direction, likely leading to collision with other satellites and a chain reaction of debris hitting satellites which then make more debris to hit more satelites and possibly getting pushed out of orbit and crashing into something and destroying everything in orbit with the aforementioned chain reaction

I think (im not entirely sure, but think) it would be less of a logistical nightmare to launch from earth where we wont have to worry about destroying a bunch of carefully placed satellites than it would be to plan out where the launch platform would be pushed to and how to stop it from hitting other things and destroying the iss in the resulting chain reaction of destruction so we could launch safely