Arguments against solipsism? Well, the most obvious one would be that everyone else appears to be implemented on very nearly the same hardware I am, and so they should be conscious for the same reasons I am.

Admittedly I don't know what those reasons are.

It's possible that there are none, that the only reason I'm conscious is because I'm not implemented on a brain but in fact on some unknown thing by a Dark Lord of the Matrix, but although this recovers the solipsism option as not quite as impossible as it'd get if you buy the previous argument, it doesn't seem likely. Even in matrix scenarios.