Barbara Harris who founded Project Prevention is a controversial crusader for social change. She wants to reduce the number of children born to drug abusing parents. Few could quarrel with that; but Barbara Harris's method - offering cash to addicts prepared to accept sterilisation or long term contraception - has raised a storm of criticism first in the US and now in the UK. Stephen Sackur asks whether Project Prevention is little more than eugenics dressed up in a cloak of compassion?