It's not like giving up your 5th Amendment rights.
When in court or testifying before Congress, if you answer [link|http://en.wikipedia.org/wiki/Taking_the_fifth|any] question you can't then assert your right to avoid self-incrimination.
But if you consent to let someone come into your home, you don't automatically consent to let them do what they want. If you let someone give you an examination, you don't automatically consent to let them sexually assault you. More specifically, consenting to a breast exam doesn't strike me as automatically consenting to a genital exam.
And [link|http://en.wikipedia.org/wiki/Consent_%28criminal%29|consent under false pretenses] isn't really valid consent, is it?
Hence, most states have laws which criminalize misrepresentations, deceptions and fraud. These are situations in which a victim may have given apparent consent to parting with ownership or possession of money and/or goods or generally suffering a loss, but this consent is treated as vitiated by the dishonesty of the person making the untrue representations.
Cheers,
Scott.