... 4. franklinmonroe does bring up a good point about discrepancies between the LXX and Hebrew MT. Thus we must default to the Hebrew MT since the LXX is a translation of the MT. Selah is extant to the MT. Why should it, thus be, excluded? ...
I'm not planning on spending a lot of time on this but I did a little checking into the Hebrew of the Psalms as found in the Dead Sea scroll fragments. In those Psalms in which the DDS actually preserved a superscript they are nearly always in full agreement with the MT reading. However, it seems there are a few variants of the Psalm headings between the DDS and the MT.
For example, at Psalm 33 (page 522) in Abegg, Flint, & Ulrich's
Dead Sea Scrolls Bible English translation from 4QPs
q there is a superscription "
Of David. A Song, a Psalm" that is supported by the LXX but not found in the MT.
The MT is a rather later and standardized text as compared to the DDS or the LXX. Why should they be excluded (especially where they are in agreement)? That is, if we are to be concerned about the removal of the word "Selah" from the main text to a footnote, shouldn't we we be equally (or more) concerned about including all genuinely original text?