An interesting dilemma. The courts here in the US have set precedent that one cannot forcibly take the DNA from another individual without that individual's consent (we just saw a situation where police unjustly arrested and detained a nurse after she refused a request for a blood draw on an unconscious patient while reminding them of this law).

However, there is no protection for the individual if the DNA is obtained in a way that is non-coerced (ie: rooting through a person's garbage for something that might contain a hair or saliva sample, or, in your example, semen from a used condom).

I whole-heartedly agree that one should not be able to deliberately use another person's DNA to create a new life without that person's consent, and use of contraception in any form should very much make it clear that the intent was for pleasure, not for procreation.

Be interesting to see what the legal system makes of this once we see a case of it. You know it can't be too far away...