Unfortunately pilots don't have a whole lot of options to exert meaningful pressure on aircraft manufacturers.
If a group of pilots came together to declare an aspect of a plane's functionality as unsafe, wouldn't that send strong signals to the public, governments, ICAO, etc? Even if those signals were ignored initially, they could become more important later if an accident occurred in which the same functionality is (or "was"?) involved. At that time, the media groups, great lovers of scandal and tragedy, would come out and say, "Functionality X contributed to the accident. These pilots warned about the dangers of functionality X back in year Y, and everyone ignored them." After that, the pilots' opinions might be more heavily considered.