In reply to Jon Dickens.

I agree with what you say about model development, but that is not the issue here. The question is about collinearity diagnostics. In a model THAT HAS AN INTERCEPT, some people argue that you can drop the intercept as a column in the design matrix WHEN YOU RUN COLLINEARITY DIAGNOSTICS. Others (including myself), argue that you need to keep the column when you assess collinearity.