People are afraid of rightwing ideologues on the Supreme Court because it means that certain cases might be reasoned from a point of view that is based less on sound legal philosophy and more on personal beliefs from the 1800s.
Not even just the Supreme Court. Federal judgeships are being handed out left and right to (often unqualified but ideological) members of the Federalist Society. It's probably the biggest thing that Trump will have done that'll affect us our entire lifetimes.
There is a proper mechanism for revising the constitution: constitutional amendment. If you want to be angry at someone for what the constitution says, then be angry at the legislators who have neglected their duty to update it.
