Can someone help me understand?

I do not understand why group members ask for opinions on gender at only 12 weeks, and with only a profile pic of the baby? How can you even tell by this? I just don't get it. You can't predict gender unless blood work is done or an anatomy scan is done. Some people get so mad about it too. It's even worse when its a pic from 9 weeks or prior. I understand the theories and such for fun but some people believe gender can actually be predicted and get so upset.