Actually, there is a fairly big body of information to support the idea that there is no other life elsewhere.
This planet appears to be very peculiar. It isn't just where it is in the system, how close it is to the sun - it's a lot of things, the existence of the moon, shape of the orbit, many many things. The 'Goldilocks Planet' idea was based on the earth being the perfect distance from the sun, and very few other planets being that distance. The assumption being life can only exist within a specific temperature range. But there's a lot more to being a life supporting planet.
Buuuut......Some of the 'why this planet is so peculiar' tends to be based on assumptions that life elsewhere would be similar to most life here - carbon based, water needing, etc. Other life wouldn't necessarily need the same things life here does. That allows for a little more potential.
But the bottom line is that most predicted and known planets are pretty hostile to life, even if the definition of life is made fairly loosey-goosey.
The thing I think is, that since a bacteria that uses aresenic instead of phosphorus is such big news, the ideas about 'life elsewhere' may well be a little too firmly based on what was thought to be possible here. I mean prior to Mono Lake, which kind of blows the cap off a lot of assumptions. Among them, finding arsenic on a planet is not necessarily a reason to pack it in and head to Wendy's for lunch.
There are theories that suggest how life could have started here, with aggregates of organic molecules called protobionts. Most people would not consider protobionts living, but the simple one celled organisms that came after them, probably would be. Experiments done under conditions that are supposed to be like what the earth was when life first formed (what is it, 3.5 billion years ago) have been able to form some simple types of structures with membranes. Being able to form proteins and microspheres and liposomes, all pretty cheery news, and supports the concept, but microspheres are intriguing as a way to deliver cancer treatments to the right spot, too.