What does it mean to have a ‘problem’ with a Gemara?! When a Gemara says something that you wouldn’t have said on your own, it means that you should ponder and intuit until it settles.
A friend once asked me regarding that Gemara, how come we would learn Tznius from a cat, why wouldn’t we learn Pritzus from fish? The answer is that we are of course the judge, as it says, Elokim Asah Es Ha’adam Yashar. We only have a hard time blazing a new way because our current situation is by default the center, or the zero value — not positive and not negative. For this, the Gemara says that when we would observe animals we would then discern the proper behavior from the natural.
The pagan nations worshipped whichever deity they thought would give them the desired benefits. There wasn’t a notion of accountability to a higher demand. This concept, that we are inherently responsible for our behavior and not just to the local king, originates in the Torah or with those that had a Messora from Adam, Shes, Chanoch, Mesushelach, Noach, Shem and Ever.
There are also certain concepts that different people never thought of as immoral, but up until our time (out time not included) are considered immoral.