Of course abiogenesis had to occur somewhere, but if we can't be sure that abiogenesis occurred on Earth itself, it means we don't have any clear idea yet of the conditions necessary for abiogenesis (apart from some a priori knowledge, such as needing to have carbon and water). Perhaps the necessary conditions are extremely strange.
We already know that Earth as it is today can't support abiogenesis, since it's not happening, and judging from the phylogenetic tree, it probably hasn't happened for more than 3 billion years. There is also a reason to believe that even if the Earth was once appropriate for abiogenesis, it only happened once, given that all life on Earth shares the same chemistry (though of course it is possible that there was simply no other way for life to be, or that there have existed other forms of life from other abiogenesis events, but that they simply have not survived).
We already know that Earth as it is today can't support abiogenesis, since it's not happening, and judging from the phylogenetic tree, it probably hasn't happened for more than 3 billion years. There is also a reason to believe that even if the Earth was once appropriate for abiogenesis, it only happened once, given that all life on Earth shares the same chemistry (though of course it is possible that there was simply no other way for life to be, or that there have existed other forms of life from other abiogenesis events, but that they simply have not survived).