No, it is not your "opinion" that 1 + 1 = 2. 1 + 1 = 2 is a statement of fact. That statement of fact may be right or wrong, but it is a statement of fact none the less.
Sorry to split hairs, but the whole opinion/fact things is a pet peeve of mine. It is common for people to think that by saying "It's my opinion", they get to say that untrue statements of fact are just as valid as true statements of fact.
An opinion is a subjective statement who's true answer can change based on who is making the statement.
A fact is an objective statement who's true answer is always the same no matter who is making the statement.
Either one can be true, and either one can be false, but that does NOT mean that false statements of fact are opinions.
So, the statement that piracy was a significant factor in the downfall of the Amiga" is a statement of fact, and therefor is either true or false. Opinion does not come into it. Now, it is perfectly reasonable to state that there is not enough information to determine whether it is true or false, and thus we have to make guesses. But, it is definitely a statement of fact.
Now, "Amiga is the best computer ever made." is a statement of opinion. This could also be wrong if you made the statement, but actually thought the Atari was better. It is just unusual for a statement of opinion to be wrong because the person making it, generally defines the true answer.
And just to make things funky, it is also possible to make a statement of fact ABOUT your opinion. e.g. "It is my opinion that the Amiga was an amazing computer!" That is a statement of fact. Why? Because it is either true or false that that is my opinion.
Sorry about the rant. As I said, the definitions of opinion and fact are pet peeves of mine. Carry on with the debates over the FACT of what effect piracy did or did not have on the fate of the Amiga, as well as the OPINION of whether copying and selling 20+ year old software is right or wrong.