They are addicted to it as a drug addict is addicted to his "high" and drug of choice. Exactly right. If Weiner stays in Congress, he'll be caught doing this stuff again. He's addicted to it. If he'd expose himself on the street, he'd get arrested.
The truth is, Weiner has probably been surfing the porn sites on the Net for years. One does not just suddenly decide to send a lewd pic to a gal and say it is "the first time" when caught and expect to be believed. His is a pattern of sneaky, perverted behavior. How many times when he was supposed to be working for the people was he visiting porn sites to get a thrill in the privacy of his office? Or at home, away from his wife's eye? Men (and women) who do this sort of thing have been hanging/lurking/participating in the lewd rooms of the Internet for quite a while. Then, often, they get brave (or bored) and just can't resist the urge to transfer that perverted desire to the world of the social networks and see if they can snare some new, innocent, and unsuspecting bait.
The incident now being discussed is probably only the tip of the iceberg in Weiner's participation in perverted passions through cyberspace.