The difference is being labeled “abnormal” by a person you know vs. by society. As a society, we used to beat children who used their left hand to write until they started acting “normal”.

The thought itself that left-handedness and right-handedness are different is not harmful. However, when you start labeling one as ‘normal’ and the other as a ‘generic abnormality’, you start shifting people’s perspectives and suddenly we get a situation where we call left-handed people “Sinister”. (The word literally means left-handed. We added the evil connotations afterwards because of the prejudice against left-handed people. We also did the same in reverse for “dexterity”.)

You might not see the harm immediately in the small scale, but it’s absolutely intended to be a step towards dehumanizing queer people. As others have said as well, homosexuality is incredibly common in nature. Most giraffe sex is gay sex. It’s just not taught in school because… say it with me… “It’s abnormal.”

It’s really not though. It’s just different, and different doesn’t mean bad.

Your argument has been used countless times in history for a number of “abnormalities” that turn out to just be differences without distinction.

“Listen, I’m a supporter of red-heads, but don’t we basically understand that it’s a genetic abnormality? Maybe ‘illness’ is a bit harsh, but they’re just not common enough in society to be considered normal.”