Do you have a problem with people licking their plates?

I do it (obviously not in restaurants or at other people’s homes, because it’s frowned upon as ya’ll know).
I don’t see the sense in leaving a really good sauce in the plate to go to waste – i wonder if the people who use the saying “there are starving people in the world ya know” to make you finish your food will also make you lick your plate clean, because there are often many nutrients left in the sauces.
Plus! It’s good manner towards the host to clean your plate a little :P – i for one hate washing plates with lots of sauces left on it, it just dirties up the water.
So, why in your opinion is it considered rude to lick a plate? And do you agree with it?