[berkes]

As above, you are presenting as a fact that investors aren't causing increasing prices. And as above, that is both uncited and, at the very least, a highly debatable 'fact'.

Even if not the only cause (is there ever just one isolated cause in economics), investing certainly is a big part.

[speleding]

Basic economic theory says that the price is determined by supply and demand. Investors buying house does not affect supply or demand, since they will simply rent out the house.

If you claim that investors are causing a significant price increase then I think onus would be on you to cite a source.