There is no absolute on this issue. Like all things in training and education, "it depends" on a host of factors.
The fact that some people vociferously criticize the training they were mandated to attend cannot be taken as valid criticism of the training itself. The majority of people probably go into mandated training with some resistance, if they are not pre-sold on the goals/benefits. Those most resistant will usually find fault with the training -- the trainer, the content, the context, the learning design, will all come under fire. Others will come out of the experience enlightened and appreciative.
Maybe our inherent dislike for being forced to participate in training is a throw-back to our school days. How many of us appreciated mandatory attendance of classes at school? How many of us ran down the teacher, the content, the relevance of the learning, just to rationalize our desire to be elsewhere? Where schooling is not mandatory, a nation declines. The same may be true of training in a company. A corporation has goals, the achievement of which require certain competencies. Each employee cannot be expected to automatically align his/her personal training needs with those of the company, and there are bound to be fundamental disconnects.
This is particularly true in times of change, and it may well be that those individuals most resistant to change are the ones least likely to participate in required training voluntarily.