I understand absolutely your feelings and frustrations. The fact is that only arround a third of women can reach orgasm through penetration alone with no 'exterior' (vulva) stimulation whatsoever. Less than 20% can rely on vaginal penetration alone to reach orgasm every time.
There is nothing wrong with you - perhaps there is something wrong with the lovers you choose or feel attracted to for whatever reason, or perhaps you anticipate that your sexual 'performance' will be regarded as a measure of your love for your partner.
By the way, stimulating your vulva and external clitoris (or anything else) by your own hand while making love (or before making love, as part of private or partnered pleasure/ foreplay) is not masturbation - it is part of true love-making. The ultimate goal of love-making should not be orgasm for either partner.
(For the sake of information - masturbation used to be a taught art in many cultures as a necessary skil for self-loving)
To me orgasm and the effort to reach it is the ultimate vulnerability. I have also 'fucked' a great many men (and women) mostly without love being present in a real way and in 99% of times with no orgasm (I am damn good at faking it for the sake of ending it). No, I have never had a vaginal only orgasm.
The idea of the vaginal-only orgasm is perpetuated by commercial porn. While I am sex-positive, I hope that the truly sex-positive will eventually make true sex as performed by true amateurs (very few) the preferred porn by the informed for the uninformed.
I also believe that real and patient masturbation and experimentation without guilt, catalysed by an essential need to love oneself, may feed one's ability to respond to / be vulnerable to the physical love of another - if the fears are spoken.
Also know, that in my (embarassingly vast) experience of pleasuring others I have found that women who cannot reach orgasm by penetration alone (like me), often reach much stronger orgasms and are most likely to be multi-orgasmic, perhaps with some greater effort.
This may be a fleeting statement - but it is my experiential view.
As usual, I am babbling, and it probably became contradictory and confusing..
Please feel free to contact me.
I have to admit that I have not read most of the replies to your original quote and do not know whether I am repeating or conflicting anything mentioned by members earlier.
"Confusing monogamy with morality has done more to destroy the conscience of the human race than any other error." — George Bernard Shaw