Every Martial Art will have criticism. Many of them are not true. For example, people say:
Taichi is not a martial art, it's too slow, it's more for health.
Aikido doesn't work since nobody is going to grab your wrist like that.
Wing Chun doesn't work since it has no grappling.
MMA is limited to rules, it only works in the ring
Kung Fu is too flashy.
Boxing has no kicks.
Taekwondo is only kicks (not true)
Judo cannot handle multiple opponents
etc......
Wing Chun is not alone. Every martial art has critics.
So why do some disrespect Wing Chun?
1. People believe in Bruce Lee too much for their own good! Just because a famous person said something, doesn't mean they are always right. You should find out yourself it it's right! People may misinterpret what Bruce Lee says and it becomes a rumor. Some people think that Wing Chun is bad because the all mighty Bruce Lee quit Wing Chun.
But, Bruce Lee did not had a choice. His father send him to the U.S. There are no Wing Chun classes in the U.S at that time. Bruce Lee was strong and fast, and he can easily just smash through his fellow students in Chi Sau, but one student noticed his weakness. His legs! He over-commit his force, so he could easily be off balance when practicing Chi Sau.
His Jeet Kune Do, either intentionally or by coincidence, covers up that weakness. It's translated as "The way of the intercepting fist or foot". That concept is directly from Wing Chun. They concept of letting your opponent attack first, but you hit him first! This requires A LOT of PRO-TIMING!
Wing Chun is a very personal art. It can and should be adapted to one's environment. Some say Bruce is still a Wing Chun guy since JKD is not too different., but some say he is a JKD guy and banished Wing Chun from his life.
2. Wing Chun's popularity can be it's own downfall. Just like how popular Karate or TKD is in the U.S, there are many people who mis-teach Wing Chun due to their lack of experience and knowledge. So as those mis-teaching get's pass on to the new generation, things go bad! And people then dislike that fake-version of Wing Chun. Chi Sau is OVERLY-emphasized for most classes. While classes do have sparing, some do not. Sparring is important. Some do not even know what the movement of the forms truly mean. No matter how perfect you are at the forms, it's useless if you do not know the purpose of the movements.
3. Some say that Wing Chun is bad since it has no counter towards grappling! However, you do not need to know grappling to deal with grappling, and you do not need to be a striker to deal with a striker. A grappler must close in the distance, likewise, Wing Chun must close in the distance against a long range fighter.
4. I don't know if Bruce really said this. But if he really did say that Wing Chun is incomplete, I don't think he should have said that, since his training in Wing Chun is also incomplete. He never learned the entire Wooden Dummy form. When he went back to Yip Man from the U.S, he wanted to film the old man practicing the wooden dummy, but Yip Man refused. Bruce never learned Biu Jee either, the third form of Wing Chun.
Bruce was a perfectionist, he never rushes. He dedicated months on a single technique while the other Wing Chun students learn 10 moves in a week.
When Bruce asked Yip Man: "Do you still see me as your student?" Yip Man responded: "Do you still see me as your teacher?"