I've always considered transgenderism to be a mental illness, though I didn't have the seething hatred and disgust I have now until recently, probably the last 5 years or so as it's become pushed further and further into the mainstream. Like many people in this thread, I was content with living and let live, I didn't really care what people did in the privacy of their own homes or however they wanted to identify. Transgenderism was a mental illness in the same way that homosexuality was a biological abnormality; I didn't think there was anything inherently wrong with it (I still don't for homosexuality, though their community is another story), but it sure as shit wasn't normal or natural and it was annoying to see people pretend it was.
Nowadays, trannies are next to impossible to avoid and the more I see and the more I learn about them the more I despise them. Everywhere you turn online, you'll find trannies and enbies and all other gender-special morons whose fantasies have been normalized into "polite society" at least on the internet. It seems like every other day someone I'm mutuals with on twitter either retweets some pro-tranny shit or troons out themselves, or a content creator I enjoy will come out as trans and suddenly all of their content will revolve around that. My feelings towards trannies is a mix between pity and disgust and hatred.
I pity the men who have been lured into trooning out due to not being "manly" enough to think they can still be men, and I pity the women who hate themselves so much that they cut their tits off and ruin their fertilities and voices with hormones because they're either lashing out from childhood molestation or they don't think they're girly enough to be women. I pity the mentally ill or autistic men and women who are tricked into transgenderism by troons trying to sell it as a magical cure-all that will solve all of their depression and self worth issues when in fact they exacerbate them. I pity the abused children who are forced down this path by their psychopathic munchie libtard parents who will likely end up 41% or murdering the parents that did this to them.
My disgust is directed at both men and women who troon out for attention or due to a fetish. I'm disgusted by incels with porn addictions who force their sissy feminization fetish on the public; they're no different from the extreme BDSM people who go outside in full leather bondage gear walking around on all fours in public spaces. I refuse to participate in their blatant fantasies even if it means getting labeled as a TERF. I'm disgusted by the men in skirts who call me "hun" and "sweetheart" and act so over the top and hyperfeminine and overly comfortable like they're trying to convince me that they're one of the girls and are just like me. Admittedly, I tend to feel more pity towards FtM rather than disgust, but I'm still disgusted by tumblr fujoshits that spend all day shlicking to gay fanfiction and yaoi who cut off all their hair and put on binders to be a soft uwu boi just like in my Japanese animes.
My hatred is towards the men invading women's spaces. I've gone through some pretty strong anti-feminist phases in my life but over the past few months I've found myself almost disgusted with how much I agree with many radical feminist talking points, at least as they pertain to trannies. I'm certainly not and never have nor will be a man-hating turbo dyke, I think the 3rd wave idea of a patriarchy is ridiculous and I'm actually a huge advocate for men's rights, but I do agree that trannies pushing themselves into women's spaces has opened my eyes to how much power some of these men have over women when they want to. Women have fought hard for their own spaces where those who dislike or fear men can be away from them, and now a bunch of men in dresses and wigs are forcing themselves into these safe havens and socially ostracizing victimized women. The amount of hate and vitriol and physical violence is so comically stereotypically masculine it's impossible to see these autogynephilic men as anything other than that: men. It's frightening to me how many women are afraid to even speak out against this outside of places like here and /pol/ and private groups, myself included. Any argument against the tranny menace is bigotry and you'll get kicked off of any platform you may once have had, and they'll brand you with the scarlet letter of "TERF" so that no one will ever listen to anything you say again. I hate having the word "woman" being coopted by delusional men or being eradicated entirely and replaced with dehumanizing misogynistic terms like "menstruator" and "uterus-haver" and "people who can be pregnant." but I feel like I can't even speak out for womanhood without being handwaved away as a hysterical feminist.
My hatred as well goes out to those pushing this shit onto children. It's disgusting and manipulative, but I know I'm really just preaching to the choir here. Kids don't even know what they want to have for dinner, they sure as fuck don't know anything about gender identity. Children shouldn't need to know anything related to sex until they're reaching the age of puberty when they should be taught the basic biological facts, not any of this genderfuildity tranny bullshit. All that does is further confuse children that are already going through the stress and confusion of growing up and changing. While I think traditional gender roles are what works best on the whole, I don't think a little boy experimenting with girl's clothes or make up makes him a girl, nor does a girl playing with monster trucks and dinosaurs and super heroes makes her a boy. This gender nonsense movement tries to hard to be progressive it wraps back around to being the very thing it's trying to dismantle by enforcing gender stereotypes so strictly that boy's aren't allowed to be feminine and girls aren't allowed to be masculine. I can only assume they're trying to indoctrinate children into transgenderism is because they're either pedophiles who obsess over children's sexualities, or they know that only children and the severely mentally ill are vulnerable enough to buy into this garbage.
Lastly, I hate big pharma for endorsing and allowing all of this shit as a means to play god on the mentally ill and line their pockets with the cash of the vulnerable. These people need help, not surgery and hormones, but all these quacks only see dollar signs and willing lab rats. They're opportunistic predators who while they may not have started this whole debacle have certainly benefited from it and continue to help push it along for their own profit rather than for any humanitarian reason. I don't believe for a second that any of these doctors or surgeons actually believe they're helping these people, unless they're braindead or brainwashed, or simply too afraid of losing their licenses due to "transphobia." Either way, they are complicit in pushing this madness and abuse.
Anyway, this ended up being a lot longer than I intended but I guess I got carried away once given the opportunity to vent in a welcome environment.
TL;DR: pretty much the same as everyone else here. It's been a slow process where the more I've learned about them and run into them in the wild online, the more my hatred and disgust grows.
community does more harm than good at this point. 
