You prove that Desmond Leslie so badly misquoted 'UFO' incidents that his work has to be completely ignored as it is not factual.
You follow up leads and sources or alleged sources for cases and find photographs "that no longer exist" or "do not exist". My books are full of these. But perserverance is what pays off. To get to the bottom of cases has taken, in one case, 30 years. In another 40 years. On average it can take 5-10 years on certain cases.
After all of this you can state the facts. "Unknown" -you say so but you should be able to offer possible solutions even if they are not currently proveable. But you have the guts to say that you have done the I and R and this is the conclusion.
If you have the solution to a case, again, you say so despite any vitriolic rhetoric from the "believers" (particularly those with a financial interest in a mystery continuing -such as Roswell). It will lose you "acquaintances" -true friends do not desert you IF you are truthful and honest.
It is a long and hard, and quite lonely, journey but it is only when you can sort out the explainable cases that you get to the unexplainable and that, my friends, is when you can get very excited.
Through hard work -the truth. No matter how weird or scary it may seem.