I hand sharpen my saws with a file and guide. I like the results I get, and don't need it done enough to justify the price of a GOOD chain grinder.
However, I've got nothing against grinders to sharpen chains. A grinder is a tool. Like most tools, if you get one of good quality, and put it in the hands of someone who knows what he/she is doing, you'll get good results.
There's a reason the cheaper grinders are so cheap. They don't have the range of adjustment to do a good job, or if they do, they are too flimsy to hold the setting needed. An operator who doesn't know what they are doing with a chain grinder can ruin a chain in a hurry, regardless of whether it's a good grinder or not.