What could be wrong with metta meditation?

 One of the standard Buddhist meditations—at any rate you find lay practitioners in America using it a lot—is the so-called "metta meditation." It's a meditation you can use to wish for peace and metta (loving-kindness) for every living being in the world, or the Universe. One version goes like this:

May I be filled with loving kindness.

May I be safe from inner and outer danger.

May I be well in body, heart and mind.
May I be at peace and completely happy.

May my loved ones and friends be filled with loving kindness. 
May they be safe from inner and outer danger.
May they be well in body, heart and mind.
May they be at peace and completely happy.

May even the people I have difficulty with be filled with loving kindness.
May they, too, be safe from inner and outer danger.
May they, too, be well in body, heart and mind.
May they, too, be at peace and completely happy.

May all beings everywhere be filled with loving kindness.
May all beings everywhere be safe from inner and outer danger.
May all beings everywhere be well in body, heart and mind.
May all beings everywhere be at peace and completely happy.

For years I've been reciting this with the Sangha I attend, and I always found it unproblematic. I have recommended it to Marie, in the hopes that it will help her blunt the edge of her fearsome bouts of anger. So far, so good.

But just recently I read a criticism of metta meditation from John Michael Greer. The context was an online journal where some reader had asked Greer's opinion of his plan to use affirmations in the New Year to wish that everyone in the world should enjoy "unexpected success." The reader said he has done metta meditations for years, and this seemed like a natural extension. But Greer objected as follows:

"One of the problems I have with metta practice is that it conflicts with the free will of the people it tries to influence. Not everyone wants to experience unexpected success—quite the contrary, many people are committed to lives of failure and will fight like wildcats if you try to get them out of their ruts. Furthermore, they have the right to the life they choose—and it may well be that they have good karmic reasons to make that choice. So, no, I don't recommend that at all."

This gave me pause. I had never thought of it from that angle before. But if you assume the principles of reincarnation and karma, it's not an unreasonable concern.

But what now? Do I have to give up metta practice? Do I sit stony-faced and obstinate when the rest of the sangha recites the verses? Somehow that doesn't sound like the right answer.

Maybe a better answer is to preserve a little nuance about my intentionality, so that I really mean "May all beings everywhere be given the opportunity to be filled with loving kindness," and the rest. Because despite Greer's point, I think there is still a value in wishing good things for others whom you dislike, even if they never take up the offer. The value is that it requires you to discipline your own heart, and to think clearly about whom you are blessing and why. If you can bring yourself to see that there are benefits to you from abandoning any malice you hold towards your enemy, then that puts you farther ahead. 

Yes, your enemy should be free to refuse your blessing if he chooses. But it still benefits you to offer it. I think it's important not to lose sight of that point.