Dear Just,
If a father goes to the neighborhood shul without a seat for his boys, maybe it is better to have a minyan on porches so that the boys can attend. No loshon hora in shul this way. The men are already home shabbos morning, and do not get intoxicated in shul.
For me, the answer is that there is no way a porch minyan is teffilah b’tzibbur, it can only be a minyan for kaddish and so on. But for you that halachic justification create this amazing koach,you can pick any of the above reasons.
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