Back to the topic of the words 'invade' and 'invasive'--the root of 'invade' is the same as for 'wade' in various languages including Latin, which is the chosen language of western medicine (for med. terminology, I mean)--to enter or go in. So, like mamarramba said, being raised by a doc has impacted her understanding of the words in a positive or at least 'no harm' way: doctors 'go into' bodies for healing purposes, it's only their method and nothing else.
But when I looked in Merriam Webster for a definition, the first handful of definitions given were all essentially negative: entering with hositility/aggression--invading a country; entering with intent to possess, as in the crime of home invasion; entering with destructive/injurious power--bacteria invades the bloodstream; tending to spread out of control, as in an invasive plant/weed; to intrude upon, as invading the quiet of the birth space; to encroach or infringe upon, like invading someone's civil rights. Only the final definition was about medical practice, giving the more neutral, factual origin of the word 'invade' as used referring to going into the body with hands/tools/chemicals for diagnosis and treatment. People so rarely use the word now, as it was used several centuries back by those speaking Old English, German or Latin. Whatever the literal meaning, the connotations (implied meanings) have pretty well taken over 'invade' and 'invasive' in common use.
I mean really--if you were planning to visit your family, would you say 'I'll be invading my parent's house next week'?

Maybe only if you had several kids (or one really rambunctious one!

) and you knew that you would be essentially taking over their home with your energies--and even then, you'd be saying 'invade' with humor, not rancor.
Also want to mention that it seems to me that even western medicine is starting to see the inherently negative elements of invasive procedures/diagnostics. I mean, it's becoming more widely acceptaed that even a vag exam or needle stick might cause an infection (apart from the medicine used in the needle)--even if these forms of invasion are 'small' and the risk very low. Not that med practice is becoming less invasive on the whole--but it sure seems to be they are being more careful about informed consent than in the past, making sure people understand that inherent risk of invasive care (well, maybe not so much with birthing women!). And for instance, things like laproscopic surgery are deemed 'safer' in general than fully opening the body with scalpels--there is 'less invasion' involved. Hmmm, not so much 'less invasion', but a form of invasion with lower risk than 'old fashioned' surgical invasion.
So yeah...we might agree to some invasions, either not believing it will be harmful (like u/s or VE), or agreeing the risk of harm is much smaller than the risk of not having the information or help received by the invasion. If we agree, then such things don't FEEL invasive--we don't feel hostility/agression, nor a loss of privacy nor any other bad thing (even if the invasion is not physically comfortable); instead we feel safer, well-cared-for, etc.
Also, in terms of mental/spiritual sense of invasion, one's relationship with the 'invader' matters a lot: you might really be uncomfortable with an on-call OB you never met before, walking in and doing a VE or suggesting treatment without preamble. You might really hate the nurse who just can't seem to lower her voice or wait for a contrax to end before speaking to you, getting your b/p, whatever. You might be perfectly comfortable with someone you trust doing those same things (or perhaps feel 'annoyed' if it's a friend, but not so much 'invaded'). Not just relationship--but also the way something is handled. If that OB-stranger comes in quietly, waits for the contraction to end, and gently introduces herself and her wish to do something, you might not be ruffled at all (and appreciate her manner, even if the invasion isn't exactly 'wanted'). Back to the giving of permission here--and to the respect for our birthing space that we want, that space which begins with our bodies/babies, and includes our personality and mood, preferences/beliefs; the individually created birth space that varies quite a bit from woman to woman.
nuff rambling for now

I'll leave it at that for the moment.