College Republican view
Since 1869, the number of Supreme Court justices has remained unchanged at nine. This number should not be increased for a multitude of reasons.
A simple analysis of American history demonstrates that when one political party attempts to alter the number of justices, it is frequently a power grab to either increase that party’s own power or to mitigate the current president’s power.
In 1801, an opposing political party in Congress reduced the number of justices from six to five. The party was seeking to deny a court seat to the next president at the time, Thomas Jefferson, according to an NBC article by Steve Vladeck. This is not an isolated occurrence; other incidences of Congress members seeking to increase their own party’s power or diminish the opposition have occurred in 1866 and 1937, outlined in a Vox article by Dylan Matthews, by either expanding or decreasing the size of courts. In each of these cases, it is blatantly evident that a partisan seizure of power was the intention. Adjusting the size of the Supreme Court could be viewed as a deliberate attempt to gain power, and would reduce the bipartisanship and legitimacy of the court.
Even Supreme Court Justice Ruth Bader Ginsburg, who is held in high esteem by Democrats and liberals alike, agrees.
“Nine seems to be a good number. It's been that way for a long time," Justice Ginsburg said in an interview with NPR. "If anything would make the court look partisan, it would be that, one side saying, 'When we're in power, we're going to enlarge the number of judges, so we would have more people who would vote the way we want them to.'”
What Justice Ginsburg said illustrates the reduced sense of legitimacy and bipartisanship the Supreme Court would retain if Congress expanded the court to gain power.