Contracts are important, but the true value of a union is in your job protection. Airlines and their managers cannot fire people on a whim and get away with it. Everyone that ASA has fired (with the exception of one who deserved it), has gotten their jobs back. That alone is worth 2% of my income. It is like insurance. You do not want to pay for it and do not realize you do not have the correct coverage until it is too late. By that time you are stuck with the coverage you have. The say an ounce of prevention is worth a pound a cure is quite true with unions.
Not everything that a union does is correct, but the collective whole is better than any negative that comes out of them. I challenge you to research all of ALPA's different committees and then make your judgement. Their aeromedical, legal, and safety to name a few are some of the best in the world. Why would the NTSB ask ALPA to work of a crash investigation if they did not know what they were doing?