Ok. Let's bottom line this discussion.
I can understand the frustration and disappointment towards your employer for not allowing you to wear your kilt to work. Wearing the kilts seems to be an innocent and fun thing to do to brighten the work day.
It is a workplace. The reason you are an employee of the company is because they feel you are capable of doing the job and facilitate the corporate goal. By continuing to push the issue, you are damaging your relationship and value to the company and pushing yourself towards the door. So, do you want this to be a pissing contest that you will loose or continue to work for this company.
We see pictures and hear stories of other members wearing their kilts to work fairly often on this forum. Typically they are in white collar jobs that employ and value them due to their intellectual contribution that tend to be a lot more tolerant and encouraging of self expression or the member is self employed. That sort of tolerance is not as common in blue collar positions that often times boil down to if you possess the skill set and your physical ability to perform the job while not alienating the coustomers. The argument of your not being able to wear your kilt to work is somehow discriminatory towards your heritage is a specious argument at best.
If being able to wear a kilt to work is that important to you, resign your position and find a job that will allow you to do so. Make sure to wear your kilt throughout the application and interview process.