The Earth is the edge case, is the point we're making. All of the conclusions and deductions about what life must be like elsewhere that use Earth as their implicit foundation are going to be overfit to the data, so to speak. Organisms on Earth converge to similar forms: dolphins and fish, bats and birds, for instance, so the form is useful on Earth is a valid observation. Therefore, we can expect to see these forms throughout the Universe is a quite a jump.
You do not know that. All available evidence points to the opposite: We have no knowledge, not even a hint, of any other physical process that could sustain life than that of Earth's carbon-based chemistry.
The idea that life could take a myriad of different forms is beautiful, but it is pure fantasy, based on no evidence at all.
The Earth is the edge case, is the point we're making. All of the conclusions and deductions about what life must be like elsewhere that use Earth as their implicit foundation are going to be overfit to the data, so to speak. Organisms on Earth converge to similar forms: dolphins and fish, bats and birds, for instance, so the form is useful on Earth is a valid observation. Therefore, we can expect to see these forms throughout the Universe is a quite a jump.