Uhh wrong! What gives you that idea???
If engine braking was bad, why do most forms of commercial vehicles come standard with a retarder system that is SPECIFICALLY designed to do this and that the brakes alone on these vehicle are not designed to continually be used in normal driving and will overheat. Semi's HAVE to engine brake down hills when fully loaded, the air brakes alone will overheat and fade.
The only issues you could run into with engine braking (that I can see) would be syncho wear if you do excessive downshifting. The older carbureted motors could cause more cylinder wall wear due to pulling extra fuel in when braking, however this is not an issue with fuel injected engines which the idle fuel is precisely measured, and especially on newer models that cut fuel altogether when you are engine braking.
All that you are doing there is using the force that it takes to compress the air/fuel mix as a braking force, this force that is exerted is MINUSCULE compared to that of an engine at full acceleration.