The Sole-Means Principle for Permissibility: If the only means X has of doing Beta is doing Alpha , then it would be permissible for X to do beta if and only if it would permissible for X to do alpha.
If the Sole Means Principle (SMP) is correct there are far reaching consequences and Thomson does not hesitate to use it to draw large scale conclusions about rights and morality.
Here is one of her examples. You are standing on your property and observe that Smith is about to walk on your newly sown lawn. Would it be permissible for you to tell him to stop? Indeed, to yell loudly at him , "Stop!", if that's what it would take to get him to stop? You might think so. It is your lawn after all. You have property rights and isn't it always permissible to enforce your rights? Shouldn't we agree that:
(r ) If A has a claim that B not φ then it is permissible for A to prevent B from φ -ing.
"No", says Thomson. Suppose that we change the story. Suppose there is someone else, Jones, in the picture. Jones is standing, not on your property, but nearby at the edge of a cliff. As before, Smith is about to trample your grass and the only way you can prevent him from doing so is to yell, "Stop!". The thing is, Jones is so skittish that if you yell, Jones will jump. And if Jones jumps he will tumble down the cliff to his death. And suppose (somehow) you know all this.
In that case it is clearly impermissible for you to yell "Stop!". You would be killing poor innocent Jones. But given that yelling is the only means available to you to prevent Smith from walking on your lawn it follows from SMP that it is, in this case, impermissible for you to enforce your claim. Thus, Thomson concludes, (r) is false.
Now I think (r) is true. It is a core claim of Retributive Ethics. But I agree that in this case it would be impermissible for you to yell "Stop" because that would kill Jones. So I agree that, in this situation, you have no morally permissible means available to you for preventing Smith from walking on the grass. But I think, nevertheless that it is permissible for you to prevent Smith from walking on the grass. You have a morally permissible end, but no permissible means to achieve it. I reject SMP.
So let me give you seven (7) arguments that SMP is wrong.