We can let the courts decide if a particular lawsuit is "frivolous" or not. Everyone has the right to a vigorous legal team fighting for their rights in court. Putting pressure on law firms because of who they represent is indefensible.
Law firms can also decide if a case is worth it or not. Here's what a federal judge said about a case yesterday in PA:
“This Court has been presented with strained legal arguments without merit and speculative accusations, unpled in the operative complaint and unsupported by evidence, In the United States of America, this cannot justify the disenfranchisement of a single voter, let alone all the voters of its sixth most populated state. Our people, laws, and institutions demand more.”
It wouldn't make sense for any reputable law firm to present a case like this in federal court, there would be immediate damage to their reputation and possibly legitimacy.