Anyone who doesn't get why this is a big deal needs to think about it more. When an active citizen writes to an elected official about politics, it is a breach of public trust for the official to respond with an unwanted and unsolicited picture of their genitalia.
I could care less about Representative Weiner's private life, and how many photos of his dong he sends to his various sweethearts and online flirting buddies. Sending unsolicited photos of his dong to random citizens who are just trying to engage with the public work of the Congress? Not OK.