Generally, unions are a necessity in this industry. Unfortunately they have done a very poor job representing regional pilot groups, with a few notable exceptions. Many regional pilots feel that major airline interests are the priority at alpa, and that regional interests are at best neglected, or worst case actually sabotaged to advance mainline interests. There have even been lawsuits filed against alpa due to this belief.
Mesa is far and away the worst large regional in the country, and they have been alpa for years...what's wromg with that picture? There are many experienced regional pilots who are violently opposed to alpa due to their own experiences. As far as alpa at the regional level, I'm a fence sitter but my previous alpa experience certainly left me with no reason whatsoever to believe, trust, or support alpa.
Skywest does not have a union because the company has historically had a very positive atmosphere and very good payscales. The pay and QOL has eroded since 9/11 and SKW is probably headed in the direction of becoming slighlty above average. If it declines too much, it is likely that alpa would get voted in but right now it seems extremely unlikely (some people beg to differ but judging by the people I talk to it's currently about 2-to-1 against).
Personally I wish we would pursue an in-house union again...it seems to work great for SWA and AA.