I'd be happy to.
I've noticed a lot of the discussion has been about rates of return. I think one of the ways to think about P3 infrastructure investments is that public dollars are not inexhaustible. While the rate of return for public dollars is perhaps lower, we can get more projects done. We encourage economic growth and jobs by getting more projects done.
The other thing I would note is that while public funding is certainly less expensive, the private sector is particularly good at identifying projects that are the most promising. Combining different sources of funding, accepting the fact that public funds are not inexhaustible and allowing the private sector to help guide the capital to the most productive uses of that capital lead to public-private partnerships that could increase economic growth.