Finding the existence of life on another planet holds MAJOR implications for many organized and unorganized religions. It would tell us whether abiogenesis and life is common, or something truly unique.
So while discovering life on another planet wouldn't answer exactly "why we are here", it would go a hell of a long way in shaping our answers to that question.
I apologize for being semantic, but I think that would answer the 'how' rather than the 'why.' I understand what you're saying though. As for the religious, well... I believe they will absolutely find a way for there not to be any major implications. New findings will be absorbed into the obfuscatory practice of apologetics.
I can't believe you like the idea of discovering alien life so you can use the discovery to troll religions. Surely there's other reasons why this is exciting?!
Even a negative finding holds important implications: if we successfully survey all of the exoplanets within 100 to 1000 light years and find no life or anything even close being habitable for humans, then it would gravely inform us of the ways in which we must preserve the Earth that we have.
So while discovering life on another planet wouldn't answer exactly "why we are here", it would go a hell of a long way in shaping our answers to that question.