Complex sentence: Most of the major airlines, whose profits were virtually guaranteed, favored the rigid system, but passengers forced to pay escalating fares were against it and were joined by communities that subsidized air service at ever-higher rates.
Split into simpler sentences: Most of the major airlines, whose profits were virtually guaranteed, favored the rigid system. But passengers forced to pay escalating fares did not, nor communities which subsidized air service at ever-higher rates.