Ironic that your question came in when it did.  While I was reading it the phone rang... and yes, you guessed it, a telemarketer.  This one was from a big bank wanting to sell me an insurance plan.  

These guys and gals follow pre-prepared scripts and have a list of 'counters' that they use for what they call 'objections'.  Objections are when you say something like "No thanks, I have a guy who handles my insurance." or "I'm not interested."  They counter with something like "Oh, thats great that you have someone who handles your insurance.  It's good to hear that you understand the value of insurance and how it can protect you and your family from unplanned or unforseen events and disasters."  Or sometimes they get spicey  like "You're not interested in protecting your family?"  The idea is to break through your 'wall' and get you open to what they have to say.

The problem here is that sales is an art.  It's not about shoving something down someones throat.  If the guy where to call and say something like, "Hey Ray, do you have a minute?  If I might just take a minute of your time to introduce myself.  My name is Joe and I am an insurance needs specialist with Bank such and such.  I specialize in helping folks like yourself learn about insurance and how it can protect you and your family from unseen disasters or events."  then STOP and let me respond, I might be inclined to participate.  Who knows what I will say, but it's simply polite to let me be a part of the conversation too.

It's rude when they don't ask for your time.  It's rude when they mis-pronounce your name.  It's rude when they don't offer something of value in exchange for your time.  It's rude when they don't listen to what you say when you do get a chance to speak...  and it's wrong to try and jam things down peoples throats not becuase someone might need it, but because the telemarketer has a quota to fill.

I'm tired of it, and you should be too.  It's horrible business practice and sadly the only reason they keep it up is becuase it works.  It doesn't work to actually sell their product becuase the product has value, it works becuase people can't say no and end up 'buying by default'.  Oh ya, they cancel later, but they give away $30 $40 or even more of their hard earned money to the big corporate entity.  It's all just numbers to them.

So... is it wrong to hang up on telemarketers?  HELL NO!!  Hang up on them, and even tell them ahead of time, "I am hanging up on you now!"