Playing devil’s advocate here...
“If someone came to a doctor and asked him to cut off a perfectly healthy arm because it just felt “wrong” for the arm to be there, should the doctor do it?”
What about circumcision? It also involves cutting off a bit of an (otherwise perfectly healthy) organ? Is that also mental illness?
Trims some skin off a body part and helps with cleanliness and, according to my doc, results in a lower rate of prostate cancer later in life. All of our boys have been circumcised; I feel like I’ve made many mistakes as a parent, but that isn’t one of them ;-).
The procedure has been done almost since the dawn of recorded human history and is safer than ear piercing.
1. Circumcision does not maim, which is to say, it does not destroy the function of an organ. The penis will still have perfect functionality; some claim there is a bit of impaired sensiivity, but others say that is compensated for by improved longer-lasting erectile function; so it's not like an amputation and more like (by way of analogy) a decorative body piercing
2. Circumcision can be additionally justified by an objective therapeutic advantage, in that a circumcised penis is provably less likely to transmit a range of STD's.
This holds true just for normal male foreskin cicumcisions, by the way; it does not apply to something radically different, which is female "circumcision" ---actually genital mutilation --- which dangerously impairs the healthy function of the sexual/reproductive structures involved.
I think the difference, among other things, is the thought process leading up to a circumcision.
Most people can objectively weigh the pros and cons of a circumcision, and make an informed decision. Not much emotion to it.
But if you listen to a transgendered person talk, they yearn an operation, and feel somehow incomplete until it is done...and it becomes a life goal. And they believe that it will ‘fix’ the way they feel about themselves.
So one is done for medical/sanitation reasons based on an informed decision...the other is an act of desperation.
What about preventative appendectomies? There's a health and hygiene REASON for circumcision whether you agree with it or not. So your comparison is way out in left field.