Are people makpid for what it says in M”B Siman 561 Sif-Katan 4 to not eat meat or drink wine on a day they see the churban ha’bayis? What other sources discuss this matter?
Note that the source of this halachah is from the idea mentioned by Tosafos, whereby “it is the norm that people avow themselves of eating meat and drinking wine on the day that they see Yerushalayim in its state of destruction.”
This is an expression of the mourning the Gemara mentions: “From the day the Mikdash was destroyed, it is proper that we should decree upon ourselves that we should not eat meat or drink wine.” The reason why this was not decreed, is that the decree would be “beyond the abilities of the congregation.”
It is not the general practice to be particular for this halachah, which is not mentioned by other poskim. However, as we see from the teachings above, it is a worthy practice.