What philosophical evidence is there against believing in non-physical entities?

[Thumpalumpacus]

For example, I've experienced under LSD the effects of synaesthesia, where I smelled things I saw, saw sounds, etc.  I've experienced lucid dreams in which I was able to very vividly and in details hear how musical instruments would blend together, something I have difficulty doing in waking life.

Yeah, under the influence of LSD, and 'shrooms for that matter, I have definitely experienced altered states of consciousness.

I really enjoy how they bifurcate my mind -- on the one hand, I have the experential mind collecting these odd perceptions, and on the other hand, I still have my rational mind (most often in the background under these circumstances, but still functioning) say, "Hey, guys, check this out. Would you record that there? What shade of green is that? Are you fucking nuts?" and so on.

I think that's one reason LSD especially gives insight into the mind's operations -- because it splits them up in real time and we are no longer syncretic beings, but devolve to each portion of the brain chasing its strong suit and laughing at the others that are tripping out ... even as it's tripping out itself and doesn't realize it.