It's not the bacteria on the chicken that's the concern. It's the bacteria that's left in your sink. If you wash meat, scrub out your sink with soap and water immediately afterward. And then of course, while people are cooking, maybe they set a wet or dirty dish in the sink temporarily, then transfer it to a dishwasher or whatever. That's how bacteria spreads.

I'm not some kind of clean freak about bacteria. If there was a benefit to washing the meat, I'd do it. But, scientifically, there's no benefit and only a possible downside. So I don't add an extra step of washing.

I gave one example above of how bacteria can spread. It looks like others have answered your question though too. Personally, I tend to be pretty clean while I cook, so I doubt washing or not would make a huge difference for me, although I don't see the point in doing it. And if you do, you should scrub out your sink afterward, depending how interested you are in food safety...personally I tend to follow food safety procedures a lot more closely when I'm cooking for others than I do when cooking just for myself.