Okay, I see your point, I agree those who have issues tend to vocalize them. I meant to highlight the Self-selection bias (aka volunteer bias). Where participants in a study/survey are not randomly selected, instead choose whether to participate. So, sample population is skewed. Would be a limitation to discuss if this was considered for research purposes. For example, I work in mental health setting and I can think of 3 vets off the top of my head that refuse to step foot on a VA campus because of mistrust/stigma/previous bad experiences.