A handshake means something, but it means a hell of a lot less than a contract. ACMI carriers are more than happy to put the screws to pilots when it suits them, as my former co-workers who joined Kalitta and Omni in the Bad Old Days can testify. If an employer cannot offer terms and conditions sufficient to attract and retain newhires in the current environment, it is not a failure of the employee if he or she approaches their job search with the same pragmatism on display by every corporate manager in the country.
An employment offer is not a suicide pact. ACMI carriers are currently only investing enough in their workforce to make themselves attractive prospects until "something better" comes along. Their dissatisfaction comes from the fact that "something better" is coming along a lot faster than it did in 2001 or 2008.
I have worked as an independent contractor for years. I own and manage a small business. Contrary to snide Facebook memes, a failure of management to hire and retain quality employees is rarely a result of the moral degredation of their labor pool. Pilots in the last 20 years have had to adapt to the times at great expense to themselves and their families. I have no sympathy whatsoever for managers who refuse to do so.
I don't mean to be hostile, and I pride myself on the effort I offer my employer so long as all parties choose to maintain my employment. My particular arrangement at my ACMI employer is attractive to me on the basis of my scheduling and residential needs, and on the frankly mind-boggling speed with which I became a 747-400 captain. I re-evaluate that employment arrangement on a daily basis, and I encourage my co-workers to do so as well.