How do we know how much time/effort he put into practice, keeping in shape, etc? All we as fans can see is whether a player gives it all on the field, and Cain certainly did that during his time here.
Now, I think the criticism of his recent comments should be separated from criticism of his opt-out. One is merited, especially with how the Brewers gave Cain ample opportunity to turn it around and even then only released him when he reached 10 years of service time, while the other is completely bogus.