Rashi says this parshah is said by Hakhel because majority of torah. Many ask that only contains 51 mitzvos not Rov.
Shabbos 31a V' ahavta l'rayacha kamocho. Rashi says most mitzvos are included in this rule of bein adam l'chaveiro. Perhaps that's why this parsha contains 'rov gufei Torah'. Accordingly though we don't start new minhagim, i'd say that those we, who stand by aseres hadibros because all of torah is included in them, it would be proper to stand by v'ahavta... As well.
Rambam de'os 6.3 mitzvah to love as self & therefore praise protect & honor....& one who is 'miskabed b'klon chaveiro ein lo chelek l'olam haba'. sounds like a side note stuck in while describing the main mitzvah?
Similarly, baba metziah 58b one of 3 who go to gehinom & don't come up is one who calls another by his uncomplimentary nickname. The gemarah clearly states this refers to a case where the other is used to the name & not embarrassed by its use anymore.
why is this so chamur?
The Maharal allways explains gehinom or ein cheIek... as avadon - negative or absence. Someone who is spiritually 'present' retains that presence l'asid. Someone who is absent will be so too.
I believe the reason why the rambam brings miskabed bklon in the the ikkar mitzvah is because this is the klall here. 'BE POSITIVE with regard to others'. One who can gain a feeling of 'presence' by a witty sharp line against another - even which not neccesarilly cause pain to to his friend - is sustaing himself through negativity. he has no eternal kiyum at all - Ein lo chelek l'olam haba.
How careful we must be to BE POSITIVE. What a positive life of happy love would it be if we felt love for every Jew we'd meet! Do, Think, Talk, & Feel Positive to others & with that we should be vayichan sham yisrael neged hahar.
