I found this peer-reviewed PLOS study while reading an article from CNS News.

The study takes a look at sex-reassigned people in pro-LGBT Sweden, between 1973 and 2003. Specifically, they aim to measure “mortality, morbidity, and criminal rate after surgical sex reassignment of transsexual persons” over a 30 year period.

The setting is important because Sweden has a much higher tolerance for gay rights than other Western countries, e.g. – America. There’s virtually no dissent from the gay rights agenda in Sweden – certainly no organized dissent.

Here are the results and the conclusion:

Results

The overall mortality for sex-reassigned persons was higher during follow-up (aHR 2.8; 95% CI 1.8–4.3) than for controls of the same birth sex, particularly death from suicide (aHR 19.1; 95% CI 5.8–62.9). Sex-reassigned persons also had an increased risk for suicide attempts (aHR 4.9; 95% CI 2.9–8.5) and psychiatric inpatient care (aHR 2.8; 95% CI 2.0–3.9). Comparisons with controls matched on reassigned sex yielded similar results. Female-to-males, but not male-to-females, had a higher risk for criminal convictions than their respective birth sex controls.

Conclusions

Persons with transsexualism, after sex reassignment, have considerably higher risks for mortality, suicidal behaviour, and psychiatric morbidity than the general population. Our findings suggest that sex reassignment, although alleviating gender dysphoria, may not suffice as treatment for transsexualism, and should inspire improved psychiatric and somatic care after sex reassignment for this patient group.

So, there were higher risks of death, higher risk of suicidal behavior, and higher mental illness.

The CNS News article interviewed a Johns Hopkins University scientist who is familiar with the history of sex-reassignment surgery.

Excerpt:

Dr. Paul R. McHugh, the Distinguished Service Professor of Psychiatry at Johns Hopkins University and former psychiatrist–in-chief for Johns Hopkins Hospital, who has studied transgendered people for 40 years, said it is a scientific fact that “transgendered men do not become women, nor do transgendered women become men.”

[…]Dr. McHugh, who was psychiatrist-in-chief at Johns Hopkins Hospital for 26 years, the medical institute that had initially pioneered sex-change surgery – and later ceased the practice – stressed that the cultural meme, or idea that “one’s sex is fluid and a matter of choice” is extremely damaging, especially to young people.

[…][T]here is plenty of evidence showing that “transgendering” is a “psychological rather than a biological matter,” said Dr. McHugh.

“In fact, gender dysphoria—the official psychiatric term for feeling oneself to be of the opposite sex—belongs in the family of similarly disordered assumptions about the body, such as anorexia nervosa and body dysmorphic disorder,” said McHugh.

“Its treatment should not be directed at the body as with surgery and hormones any more than one treats obesity-fearing anorexic patients with liposuction,” he said.

In fact, at Johns Hopkins, where they pioneered sex-change-surgery, “we demonstrated that the practice brought no important benefits,” said Dr. McHugh. “As a result, we stopped offering that form of treatment in the 1970s.”

Regarding the study, McHugh says this:

The most thorough follow-up of sex-reassigned people—extending over 30 years and conducted in Sweden, where the culture is strongly supportive of the transgendered—documents their lifelong mental unrest.”

“Ten to 15 years after surgical reassignment, the suicide rate of those who had undergone sex-reassignment surgery rose to 20 times that of comparable peers,” said McHugh.

Normally, when it comes to questions like these, I think it’s best to be guided by the evidence. What good would it do to tell someone to do something that makes them like you today (“you’re so tolerant and compassionate”) if they commit suicide tomorrow? Although people today think that being truthful and setting boundaries is “intolerant”, it can actually save someone’s life. When you stop someone from going further in a direction that will expose them to harm, you’re actually doing the right thing – even if they hate you right now for disagreeing with them. (That hatred of dissent is a sign that they are wrong, by the way)