Make logical arguments to a bad faith, intentionally obtuse WOAT level poster, brehsi think the reason they should do it is because of republican conduct in this area.
republicans refused to seat a justice for a year under the pretext that the american people should get to decide in an election year. then they rammed one in in less than a month before an election because they had the power. their goal from all of this has transparently been to swing the court to the right wing and prevent the democratic party from being able to achieve and maintain political gains. the fact that SCOTUS issued a bunch of slim 5-4 majorities in support of crucial issues for the democratic party's voters like the ACA, abortion rights and gay marriage makes the prospect of a 6-3 conservative court extremely disturbing to any democratic politician or voter.
why should the democrats not add seats to the Supreme Court? its not against the constitution. it isn't any more a violation of norms than either holding a seat open for a year or ramming a judge through the month before the election (both of which were unprecedented - restructuring of SCOTUS is not). the democratic party has every interest to do this and, if they gain the Senate, no reason not to.
God bless you sir