And when there's 10,000 activists hell-bent on creating a publicity stunt for the TV cameras?  You going to invite them all in to your living room too?  

The sheer numbers are part of the problem here.  A Senator represents 5.5 million people in CO, vs around 800k for a Representative.  Activists are swarming House members too but not in the numbers going after Gardner.  And before you compare it to Bennett, remember that hardly anyone cares what Bennett says or does.  (1) he's Bennett, and (2) he's in the minority without much power.  Although if we ever find ourselves in the unlikely spot of getting to a "replace" bill that needs 60 votes after a "repeal" bill passes first, Bennett may be on the hot seat himself with conservative activists shutting down his town halls.  

Yes, Gardner has an obligation to listen to his constituents. And he offers ways for you to make yourself heard. You just don't like the ways provided, since they prevent the town hall publicity stunts.