Being a solipsist is unreasonable.

Deconstruction of Pro's arguments(1) Uncaused First CauseIn this argument, my opponent bases their argument on the unsupported assertion that the mind 'created' all things, places, etc in a way that solipsism does not argue. The mind did not actually create anything. On solipsism, the sense perceptions which are taken to be other beings, phenomenon, etc. are projections of the mind e.g. hallucinations. I will admit that this creates problems for the solipsist as far as their own origin goes. But given that something is a mind insofar as in that it thinks, it's not unreasonable that a mind (by virtue of being a functioning mind) could produce thoughts.On metaphysical origins and an "uncaused cause" solipsism does not contend to be a completely comprehensive philosophy. It is merely a theory of what can be known for sure and what cannot. On solipsism, our sense faculties can be doubted no matter how certain we feel about them. The only thing of which one may be truly certain is that their own minds exist. So owing to the skeptical nature of the position, solipsism does not have a view on the mind's metaphysical origin. But this in itself does not mean that the solipsist is wrong in their doubt. The solipsist merely adjusts metaphysical beliefs to what can be justified epistemically.(2) Argument from Likelihood/ Statistical ImprobabilityMy opponent here misinterprets the solipsist position. This argument only holds if the other 107,000,000,000 people actually existed. But the solipsist doesn't hold this to be true and so the number of people to have allegedly exist before is of no relevance. (3) Argument from Biological NecessityThe argument from biological necessity rests on a crucial fallacy which is a reliance on empirical as opposed to rational or purely logical investigative methods. This brings us to the larger argument in favor of solipsism, the fact that our sense faculties can always be doubted. It is always a possibility (no matter how unlikely one might think it to be) that we are being tricked in some way. Hallucinations are a minor example of this phenomena and so we know that the senses are not infallible (even the denier of solipsism must agree with this). However, our rational faculties are capable of coming to near certain knowledge insofar as our premises and reasoning are correct. I'll go more into this in my own positive case in favor of the reasonableness of being a solipsist. The evidence my opponent brings to the table is entirely of an empirical nature, meaning it can always be doubted and is thus insufficient in coming to a certain conclusion.The case for the reasonableness of solipsist beliefMy opponent and anyone denying the reasonableness of the solipsist position must be against the concept of epistemic certainty, for that is all that solipsism is. Take an apple or a chair or a light bulb and ask "Could that possibly be an illusion?". The answer is of course yes. It happens all the time. Our senses deceive us. Whether one is a schizophrenic hallucinating wildly or a nervous man seeing what his mind projects in a shadowy alley, it cannot possibly be denied that one's senses can sometimes be and sometimes are wrong. All the solipsist does is admit this and adjust their epistemic (and metaphysical) outlook accordingly. One can never know with certainty that anything outside of one's self certainly exists and thus one would not be justified in believing so. Written in syllogistic form, the reasoning goes as follows: P1: One is only justified in believing that which can be known with complete certainty.P2: One's self (mind) is the only thing which can be known to exist with complete certainty.C: One is not justified in believing in anything except for one's mind.Defense of Premise 1I suppose the initial bar with which the solipsist sets that which can be known is what is most controversial about the position. After all, most people think that when their eyes see something, it's justified to believe so. However, one must realize that the certainty one derives from what one's eyes register (a posteriori propositions) is wholly inferior to the certainty one derives from logical necessity or reasoning (a priori propositions) as far as certainty is concerned. It is possible that one is not registering correctly what one is looking at and thus one can possibly have unjustified belief. This does not hold for a priori reasoning. If one's logical reasoning is correct, it is not possible to hold unjustified belief. The rationalistic method of acquiring knowledge is clearly more justified and more apt to yield correct results and certainty than the empiricist method.Defense of Premise 2Upon initial reflection, nothing can be found to necessarily exist with complete certainty other than the mind itself. Even the concept of one arguing that their mind does not exist sounds like rubbish on it's face. In order to refute this premise, my opponent would need to show why something other than the mind can be shown to exist with complete certainty, certainty wherein the concept of denying it's existence is self-contradictory.Defense of the Conclusion, ValidityThe argument itself is clearly valid. Premise 1 asserted a theory of what qualifies as justified belief, Premise 2 argued what stood up to those qualifications, and so the conclusion is necessitated if the premises both hold to be true.