MaxBrenner, I would think it is a contentious issue - there are many studies that suggest for and against. Take for instance,
Harvard Gazette: Too much protein may cause reduced kidney function, which recommends an analysis of kidney-function before embarking on a high protein diet (for the older folks, that is). Though I do acknowledge that most studies which recognise kidney damage as a potential side effect note that it is an issue that should mainly concern those with a reduced kidney function, kidneys that struggle to cope with hyperfiltration..