It's the stiff out of plane rotor head that is wholly impractical for a two bladed rotor on a passenger carrying aircraft. While a stiff out of plane rotor can be trimmed with cyclic for various flight conditions, it does require more complex control laws than a simple flapping rotor head. The vibrations are a particular killer. If Nb = number of blades, vibrations in the airframe are caused by Nb +1 and Nb-1 vibrations in the rotor. The 1/rev harmonic is the largest moment, 2/rev is less, 3/rev less than that, and so forth and so on (generally speaking). This is why the current Sikorsky X-2 aircraft have 4 blades, to help reduce the vibrations relative to the 3 bladed XH-59A. A two bladed rotor would be converting the largest and 3rd largest rotor oscillatory loads into airframe vibrations. It's a terrible idea. Comically bad, actually, and made worse because the human sensitivity to vibration increases as the frequency drops. So for a given diameter rotor, a rigid two bladed rotor will have both much higher vibration magnitudes at a worse frequency than the same diameter rigid rotor with, say, six more slender blades (holding solidity constant).
A two bladed rotor also has other 2/rev sources to deal with in the edgewise direction as well and an acrobatic stiff rotor mast capable of handling the high loads from the rigid rotor won't have the flexibility to reduce the transmission of those forces to the airframe.
There have been a few rigid two bladed human sized helicopters, though they were coaxial (to brute force the control moment terms). The Hiller X-2-235 was one and actually went through some wind tunnel testing by NACA to test the idea of this coaxial rigid rotor configuration in high speed flight, but testing was stopped due to fears of high vibrations and risk to the tunnel. Bendix made a line of coaxial helicopter prototypes and they started off as rigid out of plane rotors. The helicopter line moved to Gyrodyne and had some success, but only after adding a teeter hinge to each rotor.
Anyway, it's a terrible idea. One should notice that not even two bladed tail rotors are rigid on human sized helicopters. It's possible that rotor designers have for generations been given a stream of lucrative kickbacks by various bearing companies... or... flapping is a good thing and makes for a better aircraft, despite being a little more mechanically complex.