On yesterday's post I explained the Ran who holds that the source of נותן טעם לפגם is as the gemara implies learned from the issur of neveila that deteriorates to a point that it is no longer eatable. Based on this approach, the heter for נותן טעם לפגם is not a limitation in the din of ta'am k'ikar, rather it is because issurei achila (forbidden foods) only applies when the person is benefiting from them. Therefore, the Ran concluded that if the appreciation in quantity compensates for the deterioration of quality, it would be assur since there would be an ultimate benefit and gain.
It seems to me that there is a strong support to the Ran's approach from the gemara today. The gemara tries to prove that the machlokes between R. Meir and R. Shimon whether נותן טעם לפגם is permitted applies even when the issur gives a bad flavor at the time that it falls into the heter (meaning that even under those circumstances R. Meir would forbid it). The braisa says that when yeast of chulin falls into dough (enough to cause it to rise) so that the dough is perfect, then teruma yeast falls into the same dough which causes it to have a sour flavor, נותן טעם לפגם - there is a machlokes whether it is permitted. From here we see that when issur or teruma falls in and gives a bad flavor, R. Meir would still hold that it makes the dough assur. The gemara pushes that off by saying, perhaps even R. Meir would agree that נותן טעם לפגם is mutar (when it is po'geim at the time of the mixture), but in the case of the yeast he holds that it isn't considered p'gam (detrimental). Although for eating purposes the dough is ruined by the extra yeast, it is now fit to use as a sour dough or yeast to help other doughs rise and is therefore considered an improvement, not a p'gam. The sevara seems to be that even though there is certainly a p'gam in the taste of the dough, it can be compensated for by the use of the dough for other purposes (such as rising other doughs) and therefore is considered נותן טעם לשבח. Just as the benefit for other purposes can compensate for the detriment in taste, so too the benefit of quantity can compensate for the detriment in quality and be considered נותן טעם לשבח and therefore forbidden.