My husband took over our pack just 2 years ago and I am the comittee chair. He has a very easy way to stop parents like this: He hands them an adult leader form and asks them to fill it out, buy a uniform, attend training and get involved. Most will either put up or shut up. His tactic when they speak about another pack is to say, " Not every pack is for every boy. If your son would be happier in another pack, explore that option. I would rather lose you and your child to another pack than to loose you to scouting completely." We have two packs very close in our town and each has a very different personality. Ours is much more outdoorsy and camps and hikes, the other is more academic. Whenever we are approached by a new family, we tell them to check out both packs before making a decision. You will always have unhappy people, the trick is learning when it is important and when it is just them.
Try to ease the pressure on you and your husband by getting your leaders trained and setting up a comittee. The easiest way to get voluteers is to ask people to do the things they are good at. We also assign our yearly events to different dens for completion. Tigers host the Rocket Day, Wolves host Blue and Gold( an elective to plan and help decorate a party), the Bears host Crossover and the Webelos are in charge of Pinewood Derby. This way all of our parents get a chance to help and year to year there is a learning group and a group that has already done it to use as a resource. Hope this helps, Good Luck.