I am sooooo happy to have one.
When I lived in my townhouse in Streamwood, I didn't have one.
When I lived alone, it wasn't that bad to just manually do dishes (though I HATEd it with a passion, and would procrastinate until I ran out of clean plates and silverware to use, but it was like once every 2 weeks that I had to wash) ....
Now that I have a dishwasher, it gets run maybe 4 or 5 days per week. There are four of us living there, and usually there's at least 4 or 5 plates and like 6 or 7 cups and a bunch of silverware every day as well as at least a couple of pots and pans ...
I haven't had to prewash anything ever, there are a few things that I've had to run through twice, but that's only happened when we stuffed it too full and blocked dishes from getting properly cleaned!
As far as a reason why you should keep yours, there may on may not be one, but there may be several.
If you eventually plan on starting a family and doing so at the place you currently live, then by all means keep it as you'll find it much more handy when two or more people live there. If you have company over for dinner or something, you'll find it handy, so if you invite people over a lot, it's worth keeping. Also, a dishwasher is a definite plus for selling a home. If you are planning on selling and moving out eventually, then it may be easier to sell if you keep the dishwasher.