I understood that a baseball moving at the cosmic speed limit can do lot of harm, but since photons are not comparable to a baseball so irrespective of their high speed they do not rip anything in their way. Now I want to know that why every photon, whether its of RADIO WAVES, X-RAYS or VISIBLE RAYS have same speed, even if their energy is different? Is it only because photons (of different waves) do not have REST MASS so they can achieve the cosmic speed limit? But there is another fact that they do have momentum and momentum does increase with energy then why their speed does not change?
It's because photons are massless and so they can and must move at the speed of light with any none zero amount of momentum. This means that even though they move at the cosmic speed limit they can have very little amounts of momentum.
Size is relevant. Even weak photons can be absorbed by knocking an electron to a higher energy level. If you were that small you would be ripped apart.
thats an interesting question, but photonic fields are fundamental and cannot really be compared to say a baseball. If you throw a baseball at near the speed of lightit would probably break a lot of stuff, but photons don't really effect things very much unless they are high energy. Note that high energy photons like x-rays actually do have the ability to "rip stuff apart" but they do that on short length scales. Sunlight is also capable of giving you a sunburn. However, most low intensity fields (especially at long wavelengths) will not interact at all with matter.
Let me turn your question around. A radio wave photon, with thousandths or millionths of an eV in energy, travels at $c$. Why should it be able to rip anything apart? Its energy is very small compared to any chemical bonds. That says it has only three options-be absorbed, reflect, or scatter. Reflection imparts the most momentum into the object, but it is so small it won't deflect the atom it scatters off significantly. Not quite so fast, but the air molecules that strike you all the time are traveling very fast by conventional measure, but they don't rip you apart. They carry more energy than an AM radio photon.