Cold callers are they stupid? or just pathetic losers who dont want a real job?

Its saturday morning i'm slouching about waiting for my sister to call, the door knocks and i run foward to let her in. Oh but no! its not somebody i'm comfertable with. Some clipboard hugging smily bint. I told her straight off "Sorry i thought you were somebody i was expecting or else i wouldnt have opened the door so quickly" 30 seconds later shes accusing me off being aggresive even though she called to my door and didnt take the hint that i was expecting somebody. She was trying to sell dental insurance. I have dental insurance already from my house insurance company, if i want any insurance i go out myself and shop for it i dont expect some ****** to come to my door and accuse me of threatening behaviour before running off because she lost a sale. So cold callers what is it with them? are they idiots or what.