I've been wondering about this for some years now, scientists have been trying to find alien life in paces similar to Earth, they're trying to find a place with water, decent temp, etc.
It's as if they're trying to look for humans :O, but what really confuses me is that 90% if not all of astronomers believe in evolution, so they'll agree to the fact that we (humans) are the way we are because of our environment and the way we've adapted to our surroundings in the last 100,000 years if there was no water, would that mean that we wouldn't be here right now? Through evolution we would've adapted to our surroundings and not needed water to live, wouldn't it be the something with Aliens? If there life started in a place that had no oxygen and no water, they would've just not need oxygen and water to live, so shouldn't we be looking EVERYWHERE? We are searching for places that would support us, and maybe only us, which is probably why we haven't found something yet
The argument that looking for 'Earth-like' life might blind us to finding potentially dramatically different kinds of life that might even be more common from a universal perspective is one that people have put a considerable amount of thought into.
Essentially the issue boils down this - if lifeforms arise that are completely unlike any on Earth today, then what would they be like and how would we detect their presence? Without an example of a non-Earth-like lifeform that question is pretty much unanswerable. We can (and people have) come up with rough ideas of how organisms with completely alien biochemistries might operate, but there is no real way of testing how accurate those ideas might be. What we do know however is what life on Earth is like, and one thing that every living thing on Earth needs is water, which only exists in a usable, liquid, form in a fairly narrow temperature range. Since Earth-like life is the only thing we know how to look for, that is what we are looking for. If we discover life somewhere else, such as on Jupiter's moon Europa, then we will have a better idea whether all life shares certain basic requirements or whether there are forms of life that are dramatically different from Earth-like life.