"Large telescopes are more impaired by light pollution than small ones."

Left: Because the contrast between a deep-sky object (like M42 in Orion's Sword) and the background sky is fixed, large apertures are not more disadvantaged by light pollution than small ones — the advantages of aperture are in full effect. Right: In dark skies, all telescopes perform to their full potential.

S&T / Dennis di Cicco

This claim has no basis whatsoever in truth, but it's pretty easy to see how it arose. The "logic" behind this myth is that since large telescopes gather more light than small ones, they must also collect more unwanted light (light pollution). This is true, but the real issue is image contrast. The brightness ratio between a galaxy like M31 (say) and the background sky is the same regardless of telescope size. All telescopes are equally impaired by light pollution compared to what they would show under a dark sky. A large telescope's advantages — superior light grasp and resolution — are the same under bright skies and dark ones.