Question

why is it less dangerous to be exposed to high-intensity red light than low-intensity gamma rays?

Answer 1

An EM wave’s intensity is the sum of energies of all the photons passing through a fixed area in a fixed amount of time. This is the “energy” you were thinking of when you asked the question. Things that can increase the intensity of an EM wave:

1. Higher energy photons (e.g. gamma photons instead of infrared)
2. A more concentrated beam (e.g. more photons through the fixed area)
3. Faster production of photons (e.g. more photons in a fixed amount of time)

While (1) changes the visual “colour” of the wave, (2) and (3) makes the wave "brighter”.

So, to answer your question, gamma rays are considered more “Dangerous" because their photons pack more of a punch!