I think it depends WHY you have a preference.
Do you want a girl because you have a lovely relationship with your mother and your sister and your niece?
Or maybe you want a boy because your anxiety means the voices in your head are telling you that you must kill yourself if it's a girl?
I had the latter so finding out at twenty weeks meant I would have had the opportunity to be treated for those suicidal thoughts before I had a newborn.
As it happened, the baby was the "right" sex. Instead we got the news that he was showing early signs of a condition incompatible with life.
Are you suggesting that you think some people don't think the most important thing is for their babies to be healthy?
Actually, in that moment I was thinking "ok tell me more (but at least he's a boy)".
I was SEVERELY unwell, obviously. But if you go into the gender (actually sex) preference debate thinking that it's just fussiness about pink frilly clothes and dismiss anyone as selfish who expresses any preference you risk preventing women with perinatal MH problems from being able to discuss them. Apparent irrationality or inconsistency such as not looking at USS but obsessively consulting strangers about nub theory, ring theory, bump shape, food cravings or aversions etc could be part of that.
Strong gender preference can be an indicator of MH difficulties. OP, if you think that might apply to you then now is the perfect time to talk to your midwife about it.
If on the other hand it's just a passing fancy or you're getting noise from family and friends, give yourself a gentle shake and know that babies and children and adults follow their own path regardless of our plans and hopes and dreams for them.