That is true about facts, e.g. I trust that other people have verified the fact that the earth is round.
Unfortunately, ideas like "is open-source good" are usually very difficult to turn into pure facts, and are therefore opinions. And these are usually very different depending on what different people think the world is or should be - there is no "correct" fact which I can trust someone else to verify.
Please write the sequel to my book, I will not be including my book, but someone who has read my book will provide a review.
The review may be in a language you speak (and may be in a language they speak,) and they may have understood my book, but I am a clever author and they were the cheapest reviewer I could find. They are not themselves an author, nor can they read, but they have talk to authors before and have looked at the pictures in my book (I had not realized they were there!) and asked me questions I did not understand.
Oh, and I will not correct, evaluate or pay you for your sequel but readers of my book can choose to also read your book. I can cancel or up the fee for my book whenever I feel like it, so future readers may not exist.
I would say that it is a "correct fact" that it is a disadvantage to undertake the project I suggest even though you may on occasion succeed. Similarly, I would suggest you avoid building on your own dime on a closed source framework. But hey, I can't prove that golfing in lightning storms is a bad plan, so go nuts..
Unfortunately, ideas like "is open-source good" are usually very difficult to turn into pure facts, and are therefore opinions. And these are usually very different depending on what different people think the world is or should be - there is no "correct" fact which I can trust someone else to verify.