There's no such thing as a fact. "Facts" are always opinions, often other people's.
Examples of facts actually being opinions:
"It's cold today" - my perception is that I am cold, it's my opinion, someone who's just spent six months in Antarctica might disagree.
"I've turned the central heating on to warm things up" - well, I think I did, based on my memory and my understanding of how the central heating controls work. But is there any actual hard evidence to back me up? Can I prove it? No.
"Rape jokes are never funny" - well unless I've sat down and thought up every possible rape joke that's not a fact. (I haven't obviously, and I couldn't because it would be an infinite task.)
"Ghosts/Daleks/UFOs don't exist" - just because there is no evidence doesn't mean they don't exist. On some level they must exist, because people can imagine them. But the lack of proof is meaningless, lack of proof doesn't prove anything in itself because you can't prove proof will never be found. (If you commit murder and nobody can prove it, you're still a murderer, and might eventually be caught.)
Does oxygen exist? Apparently it's a "fact" we all breathe it in and need it to survive. But I've never seen any. I can't taste it. Other people have presented evidence that it exists, but I haven't done any personal research into the matter so can only go on what other people think. Therefore if I claim "oxygen exists" it's an opinion - scientists have told me it does, and I believed them.
You can present "facts" and "evidence" and "proof" all you like, but you are doing so because you believe them to be true. By definition if you are basing their veracity on belief, they are not facts.
Think of Auschwitz, the extermination camp in Nazi Poland. For many years it was a "fact" that 4 million people died there. It is now a "fact" the figure was more like 1.1 million, possibly a few hundred thousand higher. If the latter is a fact, the former wasn't, and never was. But that didn't stop it being reported in encylopedias, history books, official statistics - the very sort of places we get our "facts" from.