Ok, then, I'll provide an argument. THC. Drugs change perception. So do concussions. Reality is quite obviously mediated.
Certainly, one might hallucinate in certain circumstances, but how does it follow that reality is mediated? It seems to me to rest on the completely unfounded assumption that hallucinations are of the same nature as veridical perceptual experience: when we hallucinate we are not experiencing material objects, what happens when we perceive is identical to what happens when we hallucinate, therefore when we perceive we do not experience material objects. First of all, I would dispute that hallucinations are qualitatively indistinguishable from genuine perceptions. It is an important indication of this that we have a meaningful word that isn't perception that describes hallucinations. If hallucinations were not different from perceptual experience then the word 'hallucination' would be applicable to all experiences. Certainly, if you were to ask anybody with any experience of drugs whether they were undergoing some kind of drug induced hallucination, he might answer "No, I'm not high". You can tell the difference between a drug induced hallucination (and I suspect all hallucinations, dreams, etc.) just as you might tell the difference between drunkenness and sobriety.
Nevertheless, let's assume that there are some hallucinations that are qualitatively indistinguishable from genuine perception, does that mean the two are identical? That is, 'of the same nature'? Clearly not. The reflection of an object in a mirror, or its projection on a TV screen might be indistinguishable from looking at the object, but we are seeing very different things in both cases. Similarly, if you tell me that lager and ale are not the same thing, does it follow that I will never be able to tell the difference (without unreasonable information gathering demands)? In short, hallucinations are not the same as perceptions.