I can't smack you. I can only give you my perspective from my point of view, as I have similar issues.
We had a level II ultrasound this pg because DS was born with a cleft lip & palate. I'm not the type to typically have an ultrasound at all, though. The reason I decided to do it was because although I have not had major fears during this pregnancy about a recurring defect, I realized that I needed the reassurance that there was none so that at the time of birth if there happened to be a defect, I could avoid any feelings of disappointment, as well as any fear that might hinder me while in labor. If you would feel reassured to know that this baby is okay by an ultrasound, then I say go for it if you think that it will aid you in dealing with the rest of your pregnancy and your labor and birth. I don't personally feel that ultrasounds are great things, but in some situations, they become necessary, even purely emotional situations. You could also work on these feelings without an ultrasound, which I'm sure you are anyway, and feel good about the health of your baby and your labor & birth despite not having had an u/s.
As for the gender thing. I personally really really really want a girl. I wanted a girl with DS, but didn't feel confident about calling the baby "she" though we did the whole pregnancy (rather than "it" or "he", my midwife mama uses "she"). At some point, I had a few dreams and became to believe I was having a boy, which I did. This pregnancy, I have been convinced possibly before conception that I am having a girl, though we did have sex on the day I O'd and the day before and two days before and four days before (we were TTC! :LOL). I feel very confident in using the pronoun "she" and do so all the time. I haven't gone so far as to not have names picked out for both genders, and sometimes I stop myself from calling this baby by the girl name that we have picked out, but I'm still fairly certain (of course, I could be wrong). Does part of me feel disappointed at the prospect of having another boy? yes. Do I feel that knowing so ahead of time will give me time to adjust? no. The reason that I don't think that knowing the gender ahead of time will aid me in not feeling disappointment is because I think the let down will actually be greater if I know ahead of time as opposed to finding out at birth. The reason I think is is of course for one thing about hormones. Actually, that's probably the only real reason! I know that the intensity of giving birth is so great that finding out at the birth will be tremendously exciting and that there won't be a huge let-down, though there may be a little let-down. I always felt a little let down that I didn't have a girl the first time, but that was also tied to having a boy with a cleft (though I'm glad he was a boy with a cleft rather than a girl with a cleft - for totally socially superficial reasons). When I would see perfect little babies out & about with their mamas, I was typically annoyed and more so when they were perfect little girls. That is of course a not-so-nice reaction to have, but the truth nontheless.
Anyway, my point is that I feel that finding out by u/s and finding yourself disappointed will just give you a lot of time without that actual baby in your arms in which to feel disappointed, rather than giving you a lot of time to adjust to the idea. I'd say it'd be better to work on not having much expectation (and probably more effective) than to work on not being disappointed. Once that babe is in your arms, you most likely won't care at all.
Also, you can have the u/s for the reassurance of seeing the baby is okay without finding out the gender. Of course, it's getting kind of late to have an u/s that's going to tell you much anyway.