If that's true then why spend billions of dollars trying to find life on other planets?
Why not spend those billions exploring and colonizing our own system and beyond? That's a surer way of finding alien life then sending out expensive probes that almost always fail.
When this comes up, I step back from the question itself and look at NASA's budget and mission. Should they be searching for extraterrestrial life at all?
Probably they should, but it shouldn't be their main reason for exploring Mars.
The question of going beyond exploring to the idea of colonizing is also something NASA needn't be involved in. The private sector will do that at their own expense as soon as property rights are established.