I agree with what you have to say, but there's consequences with presenting something about yourself to that kind of hate if you're unable to sway them. If you're out of the house at least you can just ignore it for the most part.
I came out to my parents when I was 12, the year after I was pulled out of a private christian school for letting my parents know that I was not religious. I had to deal with getting called 'faggot, dyke, queer, lesbo' and variations of 'carpet muncher' and other weirdly sexually degrading remarks by my parents and brother until I left home and moved across the country when I was 17. Most of it was from my dad, who I haven't talked to in 5 years, and my mom only came around within the last year. Out of the blue.
You're right that there can be a disconnect in how people regard the group in general vs their child. Whenever I was dating a guy she'd act so surprised that I could somehow take it personally when she called some couple disgusting faggots or something. She would routinely act surprised if I mentioned another girl in any romantic sort of way, even after I had had girlfriends. She tried to argue with me that I literally can't be bisexual, I had to be straight because I was dating a guy. (Oddly, I don't think she would have argued that if I were dating a girl, because I think she really just wished she could argue me into saying I was straight.)
On the other hand, there was no disconnect between my extended family and their beliefs on it. At one point my mom needed someone to watch my brother and I for a week; She called my cousin, who cancelled last minute after finding out I was bisexual because she didn't want me sleeping in the same house with my blood relative who was a girl around the age of 8. My mom was mad she cancelled but otherwise agreed with the sentiment.
It completely ruined my social life outside of school. My brother, a year younger, was allowed to spend time alone at his girlfriend's house without her parents there.
I wasn't allowed to have sleepovers. Regardless of whether or not they were my girlfriend. If I had a girl visiting during the day I had to keep my bedroom door open. I wasn't allowed to visit them. If I did mistakenly let slip that I had a girlfriend to my mom in a moment of thinking she cared about me and was rational, I was never allowed to see that girl again. I sometimes thought I could trust her because when I was with a boy, she was so much more assuring and open to anything I wanted to talk about concerning the relationship. I was allowed to see boys and go on dates with them.
Yeah, it could be a little step in the collective forward progress in being out and LGBT. But I told my friends before I told my parents, and had a girlfriend before they - my parents - even knew I wasn't straight, and I wish I'd just kept it that way until I left the house. I too have younger siblings - my brother is mercilessly anti-gay, but thanks to my mother's recent spontaneous change in mind and my sister's young age, she is considerably less so. If my mother hadn't changed her mind, there would never be anything I could do about it. I can't change the fact that she's teaching my sis other stupid things that I find personally and morally offensive either, unfortunately.
Sorry for the wall of text.