President Trump himself has attacked the legitimacy of the Supreme Court, and specific Supreme Court Justices. It is highly hypocritical of Roberts to only defend the conservative Justices—the ones Trump himself put in place—while not saying a word when the President attacks the court.
Roberts called Schumer's statement "irresponsible" and "dangerous."
He went on to say in his statement:
Justices know that criticism comes with the territory, but threatening statements of this sort from the highest levels of government are not only inappropriate, they are dangerous. All Members of the Court will continue to do their job, without fear or favor, from whatever quarter
Many think Schumer should have known better. Just because the President speaks in such terms does not mean that it is okay for Schumer to stoop down to his level. Others think that Trump's attacks on the Supreme Court are fine, but it's wrong for Schumer to do it.