Homosexuality is accepted pretty much in society like alcohol use and cigarette use. The standard is moderation or some sort of restraint. It can't be rampant thus classifying it as harmless.
A little drinking but not to the point you become an alcoholic. Not to where you're driving while intoxicated. It's the same way with food. Even nutritionists or physicians will permit sweets or candy in moderation or under some sort of constraint.
Less nutritional products nominally junk food, sweets, fried foods,these are acceptable and permissible as products to consume once in a while, here and there, rare occasion to a limit. Intake must be limited or else the damage and or ramifications erupt.
With a limited amount of homosexuality it is rather easy to just sit back and say it's harmless. The world's population is not a concern. Whenever possible, the rebuttal is offered of dying out.
This argument is instantly rejected on account of the reason it's unrealistic and that's as far as it goes.
If it were real world conditions, this forces a different argument. Either the reality of damage is faced or the value of life gets more nihilistic than ever.
That reality is homosexuality is accepted as it kept under constraint. With it being kept limited and overwhelmed by heterosexuality it is deemed harmless.
I believe heterosexual people that support homosexuality highly doubt and reject the idea that the majority or average relationship will not be heterosexual so what's the harm?
We can be comfortable with the "love is love" mantra. We're so comfortable not giving thought to something that will never happen right. In the back of ALL of our minds we're content and relieved of this fact. It's our safety net and we posture with acceptance of homosexuality.
We know some things are bad for us but can be fine or no harm in "moderation".