You see, the trouble is, A.DIM, I honestly don't think you are using the words "think" and "opinion" correctly.

I mean, how can you possibly think that ETi is plentiful in the universe? You can hope it, you can assume it (say, for the purposes of discussion), you can imagine it (say, for the purposes of writing a science fiction novel). But to say you think it means one of two things: you have some supporting evidence, or you are deluded.

It's the same with opinion. Suppose a pregnant woman whom I hardly know is due to give birth soon. Leaving aside complications, she is going to have a girl or a boy.

Now, can I have an opinion on whether it will be a girl or a boy? Of course not! It would be meaningless. Whereas if you said, "Well, in my opinion it will be a boy," then I would assume you are basing this opinion on something. For example, you might be the doctor who examined her, or the ultrasound scan operator, or she might have confided in you that she found out.

However, if it turned out that you didn't know her any better than I do, I would say, "So who do you think you are, giving an opinion like that? Why do you think you're in a better position to give an opinion than I am?"