They ignore the warning: “Be careful what you wish for”.
Why? Any Democrats who eliminate the filibuster will warp our electoral system so severely that the Republicans face severe and unprecedented, almost insurmountable difficulties in winning elections. But even if Republicans somehow thereafter regain control of Congress, they will “conserve” almost all of the programs, no matter how liberal and destructive, that then exist. The best that the Republicans ever do, when fully in power on the top of their game, is pause usually only partially the progressive agenda, delaying for a few years the inevitable march to outright Maoism. When last did Congress reduce spending and balance the budget? In 1954 during the Dwight David Eisenhower administration amid the deescalation of the horrid and expensive war in Korea. The deregulatory trends under Trump consist mostly in a shocking, dramatic decrease in new regulations; only a tiny proportion of the existing ultra-voluminous corpus of regulatory law ever gets repealed, even now. Republicans generally propose, pass, and preside over expanding, ever more intrusive government, just less rapidly than that under Democrats.
To take one very prominent example, what happened to the Patient Protection Affordable Care Act? After years of pouting and loud noise about ineffective, halfhearted repeal efforts, it continues almost entirely intact. Sure, Congress cut a few of its most offensive provisions, and the bureaucracy revised some ridiculous and offensive regulations, but the overwhelming majority of provisions and regulations continue in full force and effect, unaltered and unconstrained.