Yeah, you're not supposed to put them full of food into the dishwasher. It's not like the thing runs on anti-matter – it's just hot water and soap.

You’re supposed to throw leftovers out before putting dishes in the dishwasher but rinsing before is overkill and greatly reduces both time and environmental gains of using one.

Rinsing takes seconds per item, and the gain is that you don't have to clear the filters as often.

Are there any environmental gains of using a dishwasher?

when I first got a dishwasher, it paid for itself in 8 months in water bills. you might argue my dish washing technique may have been suboptimal and you'd be right, but i believe many people do dishes in running water.

Yes. It uses dramatically less water than washing by hand, if you have a full load.

Unless you rinse first, then hand washing is less water.

But why would you do that? It's a waste of time and energy, in my experience, when the washing machine does a perfectly fine (and often even better) job.

Your preaching to the choir to me. I know a very large number of people who do rinse everything nearly clean before putting into the dishwasher, they do not understand me.