As an individual who has attended numerous Arbitrations regarding different issues I can state that, in my opinion, they most certainly do add another layer to any procedure.
The question isn't one of "...if you have nothing to hide, why not?" but more "..if you are following an agreed upon procedure that has worked consistently in the past, why?".
We are speaking of only 12/13 individuals here, with no public protest providing specifics of unfairness. Even Mr. Holley made a public statement that he made a conscious decision to repeatedly not report for rostered duty.
To create a separate class of employee based upon their Union membership is inappropriate and unnecessary.