This is the kind of painting that people always seem to point to and declare that their toddler could make something better. Occasionally that's the truth, but action painting can be very beautiful and interesting if it is done by someone who knows how to paint and has a good grasp of color theory.
It's not always entirely abstract either. I've seen some very beautiful action paintings that were intended to describe a cityscape or a portrait. If anything, that would be much more difficult than an ordinary painting.
Abstract art is an attempt to make something that is itself, rather than being a representation of something else. In order for the mind to really let go enough to do this, it needs a little bit of help from the body. That's where action painting can really shine.