It only seems idiotic because you're not really seeing it as a deeply moral issue from their point of view. I don't agree, but to them it's similar to allowing

It only seems idiotic because you're not really seeing it as a deeply moral issue from their point of view. I don't agree, but to them it's similar to allowing a sex offender or a pedophile as a tenant (and conflating LGBT people with pedophiles is a time-honored tradition). Even if there's zero chance that they'll do anything to anyone, it still invokes a moral revulsion. Landlords are emotional humans like everyone else, they aren't motivated solely by rent payments.