This isn't the first time someone has considered metaprogramming in ruby to be harmful, and it won't be the last. Metaprogramming is useful when you are programming reactively against external changes that you have to account for with your code. An example I like to use is the time when I had to create attributes for an object based on external json object. So even if the json object changes its attributes, the ruby program is able to account for the changed attributes.
However, in the real world, proper use of metaprogramming is infrequent. I would even venture to say that, if you are considering doing something with metaprogramming in Ruby, stop and try to solve it without metaprogramming.
Metaprogramming is not obvious and even to the author himself, it'll become
less obvious over time. Metaprogramming often ends up ugly. This is
certainly true for someone else reading the code. It is harder to debug.
You end up having a hard time finding the code using grep or the text editor because
the code is obscured via metaprogramming.
If you must metaprogram, document it well. Let your colleagues know what you are doing. Be very open about how your metaprogramming works. And it never hurts to get a second opinion on how you can avoid doing this altogether.