I'll explain. If one says tradition must be consistent with scripture, it means one must be able to find the concept in question spelled out in scripture so one can compare tradition for consistency. If one says tradition must be not inconsistent with scripture, it means one need not find the concept in question detailed in scripture, however the concept may not be contradicted by other Bible concepts.
There is a principle that suggests that we should not expound on one part of scripture in a way that is repugnant to another. Exodus 21:22-25 When people who are fighting injure a pregnant woman so that there is a miscarriage, and yet no further harm follows, the one responsible shall be fined what the woman’s husband demands, paying as much as the judges determine. If any harm follows, then you shall give life for life, eye for eye, tooth for tooth, hand for hand, foot for foot, burn for burn, wound for wound, stripe for stripe. It is not that this passage is discussing abortion, however, it is evident in this passage that the fetus and the woman are not valued equally here. I guess it is scripture like this that informed the tradition, so we have Aquinas understanding a new value imparted to the fetus at the quickening. And just so people understand me, I do think sometimes we need to choose in difficult circumstances. The appalling situation of backyard coathanger abortions that was part of the bad old days did untold damage to many women, and clearly and entirely failed to address the problem. That being said, birth control, contraception and restraint are eminently preferable to abortion. As yet, we do not live in a perfect world.
I think you may be exaggerating what was going on actually. I don't think foetuses would have been capable of survival on rubbish tips. What were 'surviving' in Roman times were babies abandoned after natural birth. There would have been little point in expectant mothers trying to terminate their pregnancies early since Caesarean C section births most often resulted in the death of the mother. It is actually unlikely that Julius Caesar was born by C section, because his mother apparently survived the procedure. .
In other words, consistent = provably conforming not inconsistent = not necessarily provable, yet not demonstrably nonconforming