Re the specific procedure and doctor, I've done my own research. I think it's safe and it will improve my looks. Of course, it also has some costs (it's not risk-free, economic cost, post-op, etc), which I believe I have considered appropriately, and I believe the pros outweigh the cons. The question I pose here is more general.
My therapist opposes this decision. My friends, including the female ones, say I don't need it (My family doesn't know (and won't know) about it but would strongly reject it). However, I feel they can't be objective about it, and they would oppose it even if I was the most hideous living being in the planet.
Now, what do you think should be the methodology or data to look at to decide whether I should do it? Because the reason I want to do it is because I see myself as ugly. But if I had some kind of dysmorphia, I would also see myself this way.
But it seems to me that "looks" is a game you can't win. You may be in the top 50% of males now, and the surgery will put you in the top 20%. Are you going to be content with that? Or will you think that you'll really arrive if you're in the top 5%? And if you get there, will you be content with that? Or will you think that you'll really have it made with another surgery, and arriving in the top 1%?
You can't win, because even if you're in the top 0.0001%, you're still looking at others and thinking "He's got a better smile than me. He's got better hair. He's got..."
You can't win. So don't start playing that game.
I find it especially concerning that your therapist opposes it. You may not find in this what your looking to find, and your therapist maybe can tell that that's what will happen.
It's not entirely useful to rely on what the people around you say. Of course your friends say that you don't need plastic surgery. Would you stay friends with them if you decided not to follow through with the procedure, knowing they think you're ugly? If even the female ones say you don't need surgery, just compare the way they treat you to the way they treat an objectively handsome man. In the presence of a handsome man, they're either fighting an incredible urge to throw themselves at him or they're sliding into his DMs without drawing attention to it.
Having said that, plastic surgery can only do so much. The celebrities you see who have undergone procedures went from pretty to striking. Then, there are the over-done celebrities whose deformed faces you would only stare at to gawk. You think you're ugly now? At least you can blame nature for being so externally repulsive.
Let's get back to your question of how best to reason through these considerations. The methodology you use to evaluate plastic surgery is honesty. Every time you lie to yourself, your life gets worse. Good luck!
Secondly, and it may be impossible to do, you need to consider whether what you are changing is really worth it. Compare fixing or removing some deformity or growth to a minor change to geometry. There is definitely a difference in motivation in either case, and thus a difference in mental outcome. Looking to other cosmetic surgeries, we see that there is a percentage of people who are unhappy inside and become addicted to surgery, chasing some ideal. We also see suicides in some transgender people who opt for surgery as it doesn't fix how they feel inside. You need to meditate on this and ask yourself, very deeply and seriously, whether achieving what you want will leave you satisfied? You also need to consider outcomes with less than total success. This isn't Photoshop after all. Reflect on how you may feel about it in 10 years, 20 years, etc.
https://en.m.wikipedia.org/wiki/Psycho-Cybernetics
from wikipedia:
Maltz found that his plastic surgery patients often had expectations that were not satisfied by the surgery, so he pursued a means of helping them set the goal of a positive outcome through visualization of that positive outcome.[3] Patients thinking that surgery will solve their problems is an example of the XY problem. Maltz became interested in why setting goals works. He learned that the power of self-affirmation and mental visualization techniques used the connection between the mind and the body. He specified techniques to develop a positive inner goal as a means of developing a positive outer goal. This concentration on inner attitudes is essential to his approach, as he believes that a person's outer success can never rise above the one visualized internally.