Etiquette is a most useful tool to assist people of independent thinking, different cultural and ethnic origins, and for life tested individuals to suspend for the moment, their particular biases, beliefs and boundaries, for the good of harmonious and respectful social interaction with one another. The human species is the only one I am aware of that finds this to be useful and important.
Nonetheless, such standards of etiquette are at best, arbitrarily determined, culturally specific, and never intended to be an all inclusive invitation for anyone to join without condition or consequence. In other words, they are primarily designed to discriminate amongst potential participants in a specified social function or activity. You either comply with such standards, willingly or not, or be potentially ostracized and banished from further involvement with the specific privileges and activities defined by such arbitrary and inherently unfair boundaries of applied etiquette.
From what I know or think of the Founder of Aikido, he would probably dismiss the entire conversation of "bowing" as a silly distraction to the goal of his Aikido, which is to create and maintain an environment where anyone who is honest and willing to work through differences of style, experience, preferences and misunderstandings, can find common ground in the generous capacity for tolerance and compassion expressly to be found in his Aikido.
When we make such a "big deal" over a singular point of required etiquette, we face the real risk of ignoring and perhaps losing the very essence of why we gather together to train. It is not for the reason of reinforcing mandatory standards of behavior, as much as allowing ourselves to remain open to new and sometimes challenging points of reference different from ours. We are in effect taking our eyes off the goal of growing together in Aiki through the medium of respectful, and open hearted as well as open minded training. It is perhaps in this way of reaching out to one another through such training that we are open to finding common ground on matters not necessarily tied to training, but to the essence of how we agree to go along to get along.
I have had several instances of earnest and well meaning people share with me their reservations of bowing to the shomen, who in every other way, were respectful, considerate of each other, and committed to training in good faith with the rest of the group. If I had capriciously terminated their membership, it would be my dojo, myself and my sense of the Founder's Aikido that would have suffered an irreparable loss. The fact that I did not yield to such an arbitrary and short sided reaction has resulted in excellent students of Aikido, and the maintenance of mutual respect and harmony in my dojo.
Perhaps a frank and quiet discussion of the reasons for the traditional trappings of common dojo etiquette would be the first order of business with such a troubled member, and agree on some alternative means acceptable to all, that would take the place of bowing to a shomen or kamiza, which never has guaranteed the true heart and intention of the individual anyway.
The late Shoji Nishio Sensei wrote of "Yurusu Budo", which I take to be "acceptance" of a temporarily unsatisfactory situation, while a universally fair and acceptable solution is being honestly and compassionately worked out through genuine Aikido training and synergistic interaction.