If the objection made is obviously wrong, you should just ignore it, since everyone (else) will understand why it is wrong. It costs you nothing; you have no obligation to correct the person (and in any case, someone else may do it for you.) If the objection is wrong but not obviously wrong, then you should anticipate this and make the case in your original post. If you neglect to do so, then a lot of people are probably making the same mistake, and you are doing something productive in correcting it.