oomis1105 – “I specified that R’ Gershom made a TAKANAH (takana=halacha and is not just an opinion), so I did not make light of it as you implied.”
I quote (emphasis mine): “many people issued their OPINIONS… the takanah of Rabbeinu Gershom re: marriage to no more than one wife at a time, comes to mind”
“Other Rabbanim state their personal, no-halachic opinions… and some of us seem to take those opinions as Torah m’Sinai, when it is not.”
First of all, Pirkei Avos is most definitely Torah m’Sinai, as HaLeiVi pointed out. No two ways about it.
Secondly, just because something is not a chiyuv does not mean it is not part of the Torah. There are two levels to Torah observance: the mandatory, and the optional. The optional parts of the Torah are there for the people who want to go the extra mile in fulfilling the ratzon Hashem, and want to be as close to Hashem as possible. These are the people who go lifnim min ha’shuras ha’din, follow Pirkei Avos, and are constantly working on themselves. These people are called chasidim, those who go above and beyond the letter of the law (not to be confused with the relatively modern chassidish movement, which borrowed the term).
Chumros, by the way, are also included in the “optional” part of the Torah. True chasidim never take a chance of not fulfilling a mitzva or of being oveir an aveira, so they make sure to do it according to all shitos.