Not as friendly as you think, you need a a lisence to fly a microlight that alone will set you around 5k€ you also need to register your aircraft and have pay an insurence.France is one of the most microlight-friendly countries around. I did my microlight license (brevet ULM) fifteen or so years ago and really enjoyed the relaxed atmosphere of the microlight clubs, the grass strips, etc. The exam was a written test, multiple choice, the practical test was done by my own instructor, and my license is good for life. Folks in neighboring countries often register and store their aircraft in France because there is less paperwork. I don't see why you'd want to be an "outlaw" pilot in France as the system is not onerous at all.
Thats allot to pay to fly an airplane that cost 1500€ to build and fly it just for fun.