Thanks for your post exo. By all means let's pick the knits. It is subtle but important to nail these issues down. So here is how I came to my present view. The stigma that you identify is a byproduct of minds that will view the topic that way no matter what term is used. So I asked myself this question, "Should we stop using a term that is already firmly embedded in our culture just because an element of the population likes to poke fun at it?" The sensible answer is simply "No." If people refuse to consider the topic with an open mind, then they are the ones with the problem. And that gives rise to the second question: Do we kowtow to the people who have the problem because we are afraid we might offend them? Again, certainly not! If we advocate critical thinking then it is important to be brave and if necessary face off with those who would resort to behaving poorly, or else the stigma will only persist further. One cannot rid the playground of bullies by not going to the playground. I will however grant that under certain circumstances, perhaps "Unidentified Areal Phenomena" might be used to ease some of the more reserved types into a conversation they might otherwise shy away from.
Also the two phrases UAP and UFO have different meanings. NARCAP chose UAP partially to sidestep the stigma, but they also define it differently to include phenomena that are natural or manmade. Those aren't what ufologists are mainly interested in. Ufologists are primarily interested in UFOs, and from the word's inception, it was meant to designate objects of extraordinary character, popularly believed to be alien craft. Official definitions also went on to make it clear that natural or manmade objects were not to be reported as UFOs. So clearly, we are not talking about some vague object that could be almost anything when we are talking about UFOs. However that is not to say that the word UAP should not be used. USI ( the group I'm with ) endorses NARCAP's use of the word UAP when it is appropriate. There is a healthy rationale there and NARCAP is an excellent project.
Lastly, I do not agree that we have no "clear evidence". What we ( the public ) don't have is material and scientifically verifiable evidence. But that isn't even relevant to the issue of usage. The purpose of the word UFO is to designate the topic of conversation, and topics of conversation are not required to be scientifically proven to exist first before they can be discussed. Lastly, many people are very interested in the subject and a good conversationalist who is well informed on UFOs can show how it advances critical thinking and fosters an interest in many areas of science. It would be interesting to put us both in a room full of people and kick off a discussion like this just to see if it would attract any attention. I'll bring my aluminum foil covered pyramid shaped hat and we'll see who gets taken more seriously.