Why is it taxpayer responsibility to pay for transgender operations?

Especially since they say it's not a mental illness. If it's not a mental illness then this is not health care, this is cosmetic surgery. Pay for your plastic surgery on your own dime.

When people transition, their income tends to go up because it makes us less neurotic and self-defeating.  The cost of HRT and other transition procedures such as surgery and hair removal is paid for usually by a couple of years into their lives post-transition by the concomitant increase in income tax.  Where that doesn't happen, the usual reason will be transphobia or possibly misogyny, both of which are evils which need to be defeated as it makes us less socially useful than we would otherwise be.

Leaving that aside, it's life-saving treatment.  I don't know where you are, but there are many countries where the government does in one way or another pay for life-saving treatment such as cancer chemotherapy or insulin injections for diabetics.  This is no different.  If you're living in a place where SRS is paid for publicly but insulin for diabetics, that simply means your government is socially backward and needs to get a proper health service established, so that both would be paid for.

I could say the same thing about other peoples children,   why should my tax money be paying for the boy next door to go to school,  it should be his parents responsibility to pay to educate him and then there is his grandfather,  the old bugger fell down and broke his hip,  why is my tax dollar paying for a 80 year old to be in hospital using up my tax money when clearly he does not have much time left in him anyway. 

The answer to your concern is. 

Because this is how society works. 

Society together supports the individual.  

Do so we help educate children and look after the old and frail and in the case you list a person who has found they are in need of medical intervention to right the wrong.   

Now if half the people in hospital were there for gender reassignment surgery.  I could follow your distress,  but the numbers are so low.   The truth is most of us if you asked them they could not telephone such a person right now. That is how small a group you are talking about is. 

Why is it taxpayer responsibility to bail out morons who built their houses on FLOOD plains ?

I was unaware that taxpayers in the USA paid for the operations.  I thought that it would have been your health insurance.