I think part of this conflict of values is presented in part by modern western culture as well. We are taught that lust and sexuality are good and healthy, and to believe otherwise is to be prudish and backwards.
Traditional Buddhist values tend to go in the opposite direction, and consider lust to be associated with the defilement, and with ordinary ignorant people. There are many EBT’s that contrast impurity with purity, and ignorance with wisdom.
But apart from this, is the material in the Mahāvastu not just an extension of what is already in MN 123 and MA 32 concerning the birth of the Bodhisattva? To my eyes, I see no significant difference between this Mahāvastu passage and what was already in the Majjhima Nikāya and Madhyama Āgama.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, when the one aspiring enlightenment, was born into this world from the mother’s womb, the mother by nature was virtuous, abstaining from, destroying living things, taking the not given, misbehaving sexually, telling lies and intoxicating drinks.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, from the day the one aspiring enlightenment, descended to the mother’s womb, sensual desires about men did not arise in the mind of his mother. She had risen above attachment to thoughts of any man.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, when the one aspiring enlightenment, was born to this world the mother of the one aspiring enlightenment was endowed and provided with the five sense pleasures.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, when the one aspiring enlightenment, was born to this world the mother of the one aspiring enlightenment was healthy, happy and had no ailments what so ever. She could see the one in her womb complete with all limbs large and small. Like a well completed comely lapis gem with eight facets, with a thread of blue, yellow, red, white or pale running through it. A man who could see would place it in his palm and would reflect. This is the well completed comely lapis gem with eight facets, with a thread of blue, yellow, red, white or pale running through it. In the same manner, when the one aspiring enlightenment, was born to this world the mother of the one aspiring enlightenment was healthy, happy and had no ailments what so ever. She could see the one in her womb complete with all limbs large and small.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, seven days after the birth of the one aspiring enlightenment, the mother of the one aspiring enlightenment passed away and was born with the happy gods.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, other women give birth bearing the womb for about nine or ten months. That is not so with the one aspiring enlightenment, the mother of the one aspiring enlightenment bore the womb for complete ten months and gaves birth.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.
“Venerable sir I have heard these words from the Blessed One himself and you acknowledged them. ‘Ānanda, other women give birth either seated or lying. That is not so with the one aspiring enlightenment, the mother of the one aspiring enlightenment gave birth standing.’ Venerable sir, this I bear as something wonderful and surprising of the Blessed One.