It's a personal choice - like whether or not you'll raise your children vegetarian, or let them watch TV. And behind these choices are varying degrees of fervor from parents both adamantly for and against such choices.
But ultimately every parent has to make those and other choices -- we do what we believe is the best for our children.
Me? I don't use heating pads right now because of the electro-magnetic waves (their use while pg has been linked to increased cases of leukemia in children later on).
Does that mean I am better than people who do? No. Smarter? No. More wel-informed? Perhaps. But even then, it's not definitive research. It's still theory, but one I happen to agree with.
Bottom line is I just have a different personal concern over what I view as harmful -- and it's not just based upon research or instinct, but upon things like our family history. If there's a pre-disposed tendency in your family toward cancer, then avoid all things cancer-related/causing.
If you have a family pre-disposition towards developmental probs, then maybe reconsider things like u/s during pg.
But that's YOUR CHOICE. Maybe the probs were caused by pregnant mothers getting flu shots or smoking or eating MSG or god knows what? I'm not trying to invalidate the pp who believes u/s is the cause of her child's problems. If she believes this, then it likely is and I feel bad for her

And to believe something so fervently and feel as if you're not in turn believed sucks, no matter what the topic.
But how I respond to that belief is my choice. I personally think there are far worse things that could affect my unborn child than u/s. And most of these are things people continue to do while pg without a second thought. But I also agree that in any situation, moderation is the key.
So I'm not going overboard with u/s nor did I rent a doppler, but the peace of mind for me has been invaluable and as such, I chose to have the u/s I've had. And there's one more scheduled to go and I'll keep it.
Because to me it's less risk than for instance those pg women who drink coffee every day, so I gave up coffee, because that's MY CHOICE. Don't bash me as some coffee-hater, please. I adore the stuff. I just think caffeine and ADD/ADHD are linked, yet I know I have ZERO proof -- just a gut feeling. So I don't preach about it -- I just practice it.
Make sense?