Rep. Barney Frank (D-MA) told columnist George Will and Rep. Paul Ryan (R-WI) on Sunday that Republican opposition to marijuana legalization was "a great embarrassment to the conservatives."

During a town hall-style debate on ABC, Frank demanded a response from Will about decriminalizing marijuana.

"I mean, personal liberty, if someone wants to smoke marijuana who's an adult, why do you want to make them go to jail?" Frank asked.

"With regard to marijuana, I need to know more about whether it's a gateway drug to other drugs," Will replied. "I need to know how you are going to regulate it, whether you're going to advertise it."

"Anything is a gateway to anything," Frank said, dismissing Will argument. "That's the slippery slope argument which is a very anti-libertarian argument. The fact that if somebody is doing something that's not in itself wrong, that it might lead later on to something else then stop the something else. Don't lock them up for smoking marijuana."

"What you're calling a cop-out, I'm calling a quest for information," Will insisted.

"How long's it going to last, George?" Frank asked. "We've been doing this for decades."

"I understand liberalism's aversion to information because it often doesn't go in their direction," Will quipped.

"No, I'm not averse to it," Frank shot back. "I've been studying this for a long time. You know, you're on Medicare. How much longer are we going to have to wait for you to make up your mind?"

"Let's get off marijuana," Ryan interrupted, eager to move to the next topic.

"It's a great embarrassment to the conservatives," Frank pointed out. "They want to tell people who they can have sex with. Come on, all this is big government! Who can I have sex with? Who can I marry? What can I read? What can I smoke? You guys, on the whole -- not all of you -- but the conservatives are the ones who intrude on personal liberty there."

Watch this video from ABC's This Week, broadcast Dec. 18, 2011.