Why are you so fixated on sex and rape ? We are talking about a medical procedure here.
A vaginal ultrasound is SOP in prenatal care, at least it was for all 3 of my kids.. Its used when the fetus is too small to see with an external. IIRC, it was done to determine the actual age of the fetus to get the due date, and make sure it was in the right place ( ie not tubal)
I don't think my wife felt like she was raped, I certainly didn't feel like a cuckold watching it

Well actually she had a female doc so maybe that had something to do with it. It was just one of the many "violations" along the road of having the babies.
Again, if there is a medical reason to do this in this case I don't see the issue.
If its simply there to "guilt" the person into not getting an abortion, then its disgusting and should be abolished. My feeling it's more the latter considering who is pushing this, however the rhetoric and emotional flailing from the "against" team isn't helping to clear the waters.