Drinking too much caffeine every day is not a good idea, but one coke every now and then? Sheesh, there is this thing called moderation. The risks of a soda every now and then are NOT "well documented". Most of the studies on caffeine in pregnancy are done on lab mice/rats. I gave up caffeine when we started NTNP but it IS an addiction, just as real as cigarettes, which most people have a hard time giving up. I don't blame someone for having a hard time getting off coke.
Besides, when you're told not to gain weight, your only options for drinks are diet sodas or water. (You realize juice has as much sugar as a regular coke, right?) I already feel sick most of the time, I'm not giving up the one thing that still tastes good, caffeine free diet dr pepper. My midwife said no sugar and recommended diet sodas since I hate drinking water.
As for your other "complaint", knowing the gender is important to most people. It can make the whole thing seem more real. Right now for us it's "the baby" or "it". Once we know, not only can we start saying he or she, but we can start using the baby's NAME. Maybe they don't like using green and yellow on everything. We already picked out a lot of stuff and while it does tend to have a more masculine look, we went with green & brown colors so I think they will still work for a girl.
Most people find out the gender when they're doing other tests. If you don't want an ultrasound fine, but maybe it's not your business if other people are doing what they think is best for their baby.