We finally come to the Fourth Variation:
| Step 1: | 1 | Every fetus is a person. | |
| 2 | Every person has a right to life. | ||
| Therefore | 3 | Every fetus has a right to life. | 1&2 |
| Step 2: | 4 | No being with a right to life may be killed unjustly. | |
| Therefore | 5 | No fetus may be killed unjustly. | 3&4 |
If Thomson is correct, there will only be some cases in which it would be unjust to abort a pregnancy.
| Clearly, in cases of rape the mother has not given the fetus the right to use her body, and so may justly abort the pregnancy. | |||
| What about in cases where the mother intentionally has sexual intercourse, uses contraception, and still gets pregnant. Does she not bear at least a partial responsibility for the fetus' life? | |||
| Thomson's response: | The people-seed thought experiment. | ||
| Suppose peopleseeds drift like pollen on the wind and, if they enter a home, they take root and grow into people. You don't want children, so you put screens on all the windows and try very hard to keep them out. But a hole in one screen allows a peopleseed to enter and implant itself in your carpet. | |||
| Does the peopleseed person that develops have a right to use your house? | |||
| What about cases where the mother intentionally has sexual intercourse and fails to use contraception. Does she not bear at least a partial responsibility for the fetus' life? | |||
| Suppose you intentionally left the windows and screens up on your house, knowing that there is a likelihood that peopleseeds might float in and take root. It would seem that in that case it might be unjust to kill them. | |||
| What about cases where the mother intentionally becomes pregnant? | |||
Anti-abortionists are unjustly requiring women to be Good (in some extreme cases Splendid) Samaritans. No one else is legally required to be even a Minimally Decent Samaritan, although they may be morally required.
It seems that except in cases where we have assumed a special responsibility for someone, we are not morally required to make large sacrifices to keep another person alive.