I do not think pasting public domain text needs to be cited as to source. But chapter and verses would be fitting.
I recognize that, but for those who are not well versed in Scripture, they may not recognize whether it's Scripture being posted or not. They would not necessarily know if it was Scripture, ECF, just someone's opinion, whatever.
And if they did know that it was Scripture, they would not likely be able to find it.
But chapter and verses would be fitting.
It would be courteous at the very least, but it appears that common courtesy is sorely lacking amongst the Catholic contingent.