Uh, no, people *are* born without sexual attraction. People don’t experience sexual attraction until puberty. And if they never experience sexual attraction or rarely experience sexual attraction, that’s okay too.
Frankly, I don’t think it matters what causes asexuality or any other sexual orientation, for that matter. Live and let live, if they aren’t hurting anybody.
Asexuals can be repulsed by sex, or they can just be indifferent to sex and just not be interested.
Aromanticism is not the same thing as sociopathy or psychopathy! There are other forms of love besides romantic, as Swede said. Aros can feel platonic love and familial love just like everybody else. They’re just not interested in romance, as the name implies. Aro/aces can live fulfilling lives just as everybody else can.
As for whether they belong in the LGBT+ community? I’d say they do, because they are marginalized for their orientation. They face dismissive bullshit from people like you, or even worse, some of them are forced into essentially conversion therapy or even corrective rape!