>We could then put Mars in the same category as the Moon when it comes to the life hypothesis. This is not the case - so I'd say a search for evidence of life on Mars (past or even present) is justified.
Of course searching for evidence of current or past life on Mars is justified. But there is a huge difference between searching for evidence, and declaring every anomalous discovery to be potential evidence. In addition, the hypothesis "a technological civilization has lived on/visited/probed Mars" is a minuscule subset of the hypothesis "there is, or has been, some form of life on Mars".
Of course searching for evidence of current or past life on Mars is justified. But there is a huge difference between searching for evidence, and declaring every anomalous discovery to be potential evidence. In addition, the hypothesis "a technological civilization has lived on/visited/probed Mars" is a minuscule subset of the hypothesis "there is, or has been, some form of life on Mars".