Artificial is an unfair characterization of history. The President didn't just descend from on high and grant unions powers out of magnanimity. At one point the unions were extremely powerful to the point that they were able to codify in law the rights they had attained.
Rights they had to fight for, in many cases _die_ for. Corporations and the government were not above using police, private firms to do violence, even fatal violence, to employees who were not willing to bend over backwards (unsafe, unhealthy, inhumane working conditions) for their employer.
See https://en.wikipedia.org/wiki/Commonwealth_v._Hunt . There was no law which "artificially" granted the Boston Journeymen Bootmaker's Society power. The "five or six good workmen" who would have walked out should Horne continue to be employed, were exercising their right of free association.
And, fundamentally, that's where union power comes from - the right to collectively decide to quit.
Union laws give unions specific powers, it's true. But they also restrict union power. If you oppose the artificial granting of power, then you should also oppose the artificial restriction of power, and allow "jurisdictional strikes, wildcat strikes, solidarity or political strikes, secondary boycotts, secondary and mass picketing, closed shops, and monetary donations by unions to federal political campaigns" [1] -- once-legal practices banned by Taft-Hartley and all fundamentally based in the power to collectively decide to stop working.
[1] Quoting https://en.wikipedia.org/wiki/Taft%E2%80%93Hartley_Act
Basically, I'm opposed to unions as they exist in the US because of the government being involved and "artificially" granting them power.