First to file is bad for the little guy, because the little guy doesn't have a legal team standing ready to churn out a patent. Assume a guy in his garage and an employee at a big corp invent the same thing. The guy at the big corp invents it a little after the guy in his garage. The result will be that the big corp gets the patent, because they will be much quicker to generate the patent application. The little guy will have to go through many more steps, such as obtaining a patent lawyer, obtaining funding for the application, etc. The process is also likely unfamiliar to him, which will slow him down.
Under a first to invent system, at least that guy has a chance. Under first to file, he's just screwed. A better solution would be to simplify the legal process rather than simply declaring the winner ahead of time according to some meaningless paperwork that big corps are always going to be better at.
In a sense, first to file goes perfectly with the current trend towards statutory non-intent crimes with trivial to prove elements. Lazy justice is justice denied.