This is an interesting topic, as it relates directly to our social norms and what we find acceptable and not accceptable. Gavin mentioned breastfeeding at the table. I think we should stop and ask ourselves why we find these things objectionable. What is it about breastfeeding, a perfectly natural thing, that we think belongs in a private setting? Is it a woman's breast, which we also believe should be kept private? Fine, I can accept that... except that most women who breastfeed have bras and shirts designed specifically for the purpose, and they're usually so good at it that there's hardly a chance of a "wardrobe malfunction". Now, if a woman is just "whipping it out" for all to see, sure, there's a decency issue involved... but if she's being relatively polite about it, covering up as best she can, what's the problem?
Don't get me wrong... using the restroom is a "perfectly natural thing" as well, but I'm not advocating people drop trou wherever they feel like it... there are obvious issues with sanitation involved, not to mention most peoples' delicate sense of smell.
Assuming that insulin usage is on par with breastfeeding for a moment, why do we object to it? Certainly some people are squeemish about needles or blood, and seeing these things in a relaxed setting (such as a dinner table) isn't preferred. Okay. But is that really the issue? Or is it more accurate to say that, as a whole, our society has dictated that certain things aren't discussed in polite company, and certainly certain actions aren't taken. But why? Similar to the breastfeeding issue above, if a diabetic is relatively low-key about it, what's wrong with taking care of a necessary function when and where necessary?
I think Bill V says it well when comparing insulin shots to mealtime prayer. I may not be of your religion... in fact, I may be relatively opposed to it. But am I going to object to your quiet, solitary observance of it? Certainly not.
I object, too, to the argument of children being exposed to these things. I'll go on record to state that I am no a parent, but that said, should I have a child I would not be opposed to my child seeing someone taking insulin at the dinner table. Would this result in 1001 questions? Certainly! Is this a bad thing? No! I think we should encourage our children to be inquisitive and curious (while teaching them polite manners).
Wow. I've said more than enough. But in closing, I'll restate one main point: We should ask ourselves
why we react to things more often, rather than just checking to see if our reaction is normal. Normalcy is overrated, and often just plain stupid.