Multiple sets? Why?

[UberSteroids]

Alright, I want to hear Your responses on this.
As we all know when working out our body recruits all four types of muscle fibers (with enough intensity) in the same order. So... if we take a break between the sets, the muscle fibers get their fuel, (oxygen, lactic acid gets removed etc) so they can go for another set BUT, they already have been fatiqued (damaged) in the first set and they NEED a time to recover already. So if we go for another set, the same muscle fibers will be recruited for a second set in same order... My question is what is the point of "damaging" the mucle fibers that has been already "damaged" in the first set and now require time to recover?
Because when You think about it... when You lift a 90s dumbbells on bench press, assuming this is a high intensity lifting, You can do 1 set of 7 and You failed, means You damaged muscle fibers/connective tissue perhaps and now it will rebuild/recover itself to prepare for another strike of 90s again BUT after the recovery. So the muscle will recover only to resist a 90s dumbbells. So if You do 2 more sets of 90s... how will this make the muscle grow stronger? It wont.. I think it will only take more time to recover... to get to the 90s d-bell resistance.
What do You guys think?