why would people go all the way to do Sexual Reassignment Surgery (SRS) so that they could be the opposite sex

Answer 1

Because they honestly feel that they were born into the wrong body, and they're uncomfortable in their own skin.

Answer 2

You have sort of answered you own question by asking it.
Why would we go all the way to do sex reassignment?
The answer is so that we CAN BE the "opposite sex" so to speak.
It's not easy, waking every day in a body that feels wrong, to live and work in a society that treats you as a social role which feels uncomfortable and incongruent with your own sense of identity.
People do not choose to be transsexual and there is emerging evidence now that there is a biological basis of gender identity which may explain why transsexuals sense of gender incongruity is so deep rooted that it cannot be changed.
Sex reassignment surgery is really the best palliation one can obtain when suffering from Gender Dysphoria as it is easier to change the body than to try and brain wash somebody's mind to produce social conformity but a very unhappy individual.

The nearest I can get to explaining that to you is to suggest you close your eyes and imagine how hard you would find it if you woke up one day with the exact thoughts and feelings you have but the body and life of someone of the opposite sex. That is how transsexuals feel all the time, until they can get sex reassignment to become more congruent with who they feel they are.

After all, men don't ask women why they want to be women, and women don't ask men why they want to be men usually do they? They just assume you are one or the other and accept you as that, the pain of transsexuality arises from the realisation that your own sense of self doesn't match that social expectation.

Answer 3

becase some people believe they were born the wrong sex. if you want to understand it, watch the movie "a girl like me"

Answer 4

those people are really desperate