In Masechet Soferim 16 (and I believe in the Yerushalmi too) it is written: א"ר יהושע ב"ל הדא אגדתא כתוב בה הכותבה אין לו חלק לעולם הבא והדורשה מתברך והשומעה אינו מקבל שכר Whoever writes down Aggada has no shade in Olam Haba, whoever expounds on it is cursed, and whoever listens to it gets no reward.
How are we to interpret this? Does this imply that all study of Aggada is worthless?
I'm not sure what to make of that that statement; however there are many Gemaros and Midrashim which talk about the great importance of learning Aggadeta.
The Sifre (Ekev), talks about how Aggadah brings to recognition of G-d; Avos Derebi Nassan (1,29) declares that "anyone who doesn't know Midrash, hasn't "Tasted" fear of G-d; and the Gemara in Bava Kama (60B) records a fascinating story which indicates that Halacha and Aggadah are equally important faucets of Torah.
Furthermore, the Talmud Yerushalmi (Meggilah, 4,1) states that Aggadah stems from Sinai.
Even if the Talmud Yerushalmi you mentioned before is to be taken literally, it seems to be a Shitas Yochid; rejected by all the other Tannaim and Ammoraim who stress the importance of learning Aggadatah.
I recall that Rav Hirsch in his essay about Aggadata (somewhere in his selected writings), addresses this Talmud Yerushalmi, but i forgot how he explains it.
Nachalas Yakov there explains most of the statement. He brings from the Karban Ha'eida that the reason why it's improper to write it is because (in those times) it was only permitted to write down the laws of the Oral Torah because we're afraid people will do an issur, but by Aggadata there was no reason to permit it.
The one who listens to it has no reward is referring to someone who listens to it from someone who darshins it from a written source. Since he learned it from an aveira he gets no reward.
He doesn't explain the reason for being excommunicated (that's how he learns blessed, a euphemism for excommunication).
But the Radvaz (t'shuvos 232) explains "one who darshins it" to mean one who reveals the kabbalistic aspect of aggadata which shouldn't be done in public, rather from mouth to mouth.
Agaddah is only worthwhile with it's accompanying interpretation. Otherwise they are just silly stories about rabbis bowing to defeat giant frogs.
Imagine a bitter medicine that it coated with sugar. Eating only the sugar without the medicine is harmful because it rots your teeth and pancreas and doesn't give you the benefit of the medecine.
