Some people might argue that if you are taking your child out of school for a cheaper holiday, you are not acting in their best interests.
And those people would be wrong.
No, brdgrl, those people would have a different opinion from you.
No, Rhonda. They would be wrong. Some "opinions" are so uninformed as to be actually wrong, you know. I can claim that water is not wet, and say that it is my "opinion", and it might be my (very uninformed) opinion - but it would also be wrong.
The fact is that I am acting in my child's best interests when I keep her out of school. I know this, because I am privy to the relevant information. The "some people" to who you refer, are not.
They can have a different opinion about the abstract idea of whether it is a good thing to keep children out of school or not - but as the post you are responding to was about "your child" (very specifically established, my own child), they cannot make an informed judgement about that. And I am quite confident in saying that they, and you, would be quite simply wrong in your statement that I was not acting in my child's best interest.
It is curious that you think that "being wrong" and "holding a different opinion" are incompatible. It is the opinion of a great many people that evolution is untrue. They are wrong. (Of course, that's just my opinion...)