[PL 211] So it seems to you that my argument proves too much, eh?

[Cross-posted at The Philosopher's Cocoon]

Philosophers often make the following complaint:

It seems to me that, if the author were right, then s/he would prove too much.

For example, some have complained that Moore's open question argument proves too much. I take it that those who make this sort of complaint mean that the conclusion argued for seems too strong. For example, in the case of Moore's open question argument, which can be reconstructed as follows:

1. Suppose that 'x is good' is equivalent to 'x is pleasure'.
2. If 'x is good' is equivalent to 'x is pleasure', then 'pleasure is good' is equivalent to 'pleasure is pleasure'.
3. But 'pleasure is pleasure' is an uninformative tautology.
4. If those who assert 'good is pleasure' mean to express more than a mere tautology, then the question whether pleasure is good remains "open."
5. Those who assert 'good is pleasure' mean to express more than an uninformative tautology.
6. Therefore, the question whether pleasure is good remains "open."

the conclusion strikes some as too strong, since it means that, for any definition of 'good' in terms of some natural property, such as pleasure, it remains an open question whether that natural property itself is good.

But so what? If Moore's argument is sound, so what if the conclusion strikes us as too strong? Should the "author proves too much" objection be taken seriously?