Realistically speaking, how many attention-seekers would choose to get attention based on something that is likely to get the majority of people you tell to look at you like you're mad? It's pretty hard to be a special snowflake (I hate that term so much) when a large number of people are more than eager to roast you for it. Lupa mentions in her book numerous Otherkin she interviewed in her research that have no desire whatsoever to come out of the closet for these very reasons.
How, exactly does the person making that declaration know what's going on inside the head of the person whose identity they just trivialized? There is no proof that there even is a soul, much less proof that a soul can only have a certain sort of nature. A soul is not a matter of fact, it's a matter of belief. With no proof, I cannot prove that you aren't a dragon born into human flesh. With such matters, I take what is told me at face value. In the world of facts, the burden of proof is on the one making the claim. However, we are not dealing with facts; we're dealing with gnosis. Spiritual truths can vary widely from person to person. If your experiences tell you that you're a dragon in human skin, I cannot argue with that; I have no evidence on which to stand. And why would I even want to?
Who am I to tell you that I know more about the shape of your soul than you do?
It's all too easy to be an armchair psychologist and to denounce things that you don't understand. It's not quite so easy to be open-hearted, willing to accept and love others for who they are. It's not quite so easy to do research, to learn and be educated about people who are different than yourself. It seems to be one of the hardest things in the world to accept that there are realities and truths that fall outside of one's own understanding.
That is not to say that there isn't danger of escapism, using one's status as an Otherkin as a means for avoiding responsibility or dealing with the important challenges that everyone faces in life. Again, escapism, as well as a whole host of other maladaptive behaviours, are possible in any belief system; I've seen my fair share people praying and casting spells for jobs while not sending out a single application. There are plenty of resources, like this thoughtful article, in the Otherkin community that deal with this; nobody is more aware than they are that it might be insanity or delusion. I'm glad to see that Otherkin are aware of the potential pitfalls that they may encounter and are on guard against them. Whether or not it's escapism, it's still not my business what your identity is or why you have it.
The universe is full of possibilities that we have not even begun to scratch the surface on. Every day, new things are being discovered in the physical world, alone, not to mention the vast and largely uncharted realms of spiritual possibility. In our universe, infinite in potential, why couldn't someone be born with a soul from another species of animal, or from another plane of existence altogether? Some people believe that the position of the planets some how, some way, has a lifelong influence on their personality, fate, and even their health. Some people believe that they have conversations with entities that have no physical bodies. Some people believe that if you light some candles and burn some herbs under the full moon, that they can affect the probability of something happening halfway across the world. Some people believe they get to sit on a cloud with their old friends and play a harp when they die. How are these beliefs any more acceptable than believing that your soul comes from a non-human source?
So why not Otherkin? Honestly, it makes me quite happy to learn that there are people with all sorts of different types of souls. It means more people that I can learn from, and more potential for magic in the world. How very dull of a place this would be if everyone were identical. It's so much nicer than being in the company of cranky curmudgeons who bitch and complain about anyone and anything which is too different or too weird for their liking. I'm happy that Otherkin exist. My world is more interesting because you are in it. Thank you.
I believe in the power of belief. If someone understands that they have an Other soul, and that their Other soul helps them to live their lives more effectively, to understand themselves more fully, and to be happier in their lives, then I say, "Go for it. More power to you." If it's empowering, do it, believe it, live it. You don't need anyone else's approval to be who you are. Whoever, whatever you are, you may as well rock it.