When reading the megillah why do we pasken like Rebbi Meir?

Question

In Megillah 19a there is an argument as to how much of the actual text of the megillah one needs to read in order to fulfill the obligation. Rebbi Meir says you need to read the whole things and the halacha, as ruled there in the Talmud and codified by the Shulchan Aruch, is in accordance with him. However the gemarah in Eruvin (13b) indicates that the halacha is never like Rebbi Meir because his colleagues could not fathom his reasoning.

My question is why is there an exception made for this one halacha, to pasken like Rebbi Meir?

Answer 1

Because those general rules are not exhaustive, as the Gemara itself says (about Rabbi Shimon vs Rabbi Yehuda), "ומאי קושיא דילמא היכא דאיתמר איתמר היכא דלא איתמר לא איתמר "

The Gemara rejects this argument: What is the difficulty posed by this ruling? Perhaps where it is stated explicitly to the contrary, it is stated, but where it is not stated explicitly to the contrary, it is not stated, and these principles apply.

And, as Rashi put it:

בהדיא הלכה כרבי שמעון איתמר וכי כיילינן רבי יהודה ור"ש הלכה כרבי יהודה להיכא דלא איתמר הלכתא לא כמר ולא כמר:

That the general rule that the Halacha follows Rabbi Yehuda against Rabbi Shimon applies only where there wasn't an explicit ruling. But if there's an explicit ruling (א"ר חלבו אמר רב חמא בר גוריא אמר רב הלכה כדברי האומר כולה), the Halacha follows the ruling.