I'm not sure American conservatives understand just how rapidly and dramatically pro-labor public attitudes have shifted in recent years since the last recession. Consider the Occupy movement, the Fight for 15 movement, the strikingly prominent Bernie Sanders presidential campaign of 2016, the wave of wildcat teacher strikes earlier this year (which mostly took place in politically conservatives states that voted for Trump, incidentally). In that context, is it really surprising that the voters of Missouri voted 2 to 1 to overturn a major restriction on unions? The Supreme Court can rule what they want, but the more they rule against labor in this social environment, the more they will only prove their institution undemocratic in nature and themselves to be what they are: corrupt cronies of the rather unpopular corporate world who deserve to be replaced and to have their institution democratized (i.e. rendered elected, not appointed) and to have their "right" of judicial review abolished until such time.
And the evidence for this great change is a Missouri referendum? Overgeneralize much.
Tradition is not the worship of ashes, but the preservation of fire. ― Gustav Mahler