What is the relevance of economic growth?
World population currently is estimated at $7.3$ billion people, while world GDP at $74.5$ trillion USD (nominal). So the global average of per capita GDP currently stands at USD $10,205$, again nominal, not adjusted for purchasing-power-parity. But in any case, this number, although not negligible, it is small enough so that, even if we had absolute global equidistribution, we would hardly be in an "Affluent Society".  

This alone could justify why Growth is still the main economic target of societies all over the world: even if inequality was out of the picture, we will still be far from living really "comfortably".  

Add inequality to the picture, and one realizes that Growth is also seen as something that can help mitigate possible social tensions due to inequality: one accepts the existence of inequality easier, if ones sees his own fortunes getting better (this requires of course that everybody gets something out of Growth, even in unequal shares).