Bar Shattya:
See, e.g., Kiddushin 38b-39a (discussing whether the din of orlah in chutz la’aretz originated as a custom or traditional practice, and concluding that if it did, there is room to mattir such produce); Sukkah 44a (discussing whether the use of aravos on Hoshana Rabah is a halacha enacted by the nevi’im or a custom, and if it is a custom, no brachah should be made when the aravos are beaten); Yerushalmi Megillah 1:5 (concluding that various customs instituted for Adar 1 do not have the force of binding halacha because they are simply a custom).
The point is not that custom is NEVER enough, but that the fact that something is just a custom, without more, May not be enough to justify the continued practice in the face of strong reasons to stop it.