What's the big deal with prunes?

What's the big deal with prunes and prune juice? They are delicious, but whenever someone sees us eating them outside the nursing home that they presumably think we live in, they can't comprehend that we would willingly eat and enjoy them...

So, I ask again - what is the problem with prunes? Put put aside your misconceptions about prunes being "only for old people" and tell me what is wrong with the fruit itself.