Then you proceed to learn about CPI in detail for the first time, and use your incomplete understanding to refute mine.
I've been down the rabbit-hole on CPI and learned a lot (partially from someone else on HN, who also probably wasn't an economist). The Wikipedia page is pretty thorough for US CPI [0]. The high-level idea is pretty simple, and seems reasonable.
The problem is the survey itself [1]. The people contributing to the survey are one segment of Americans, not America as a whole. They are the middle class. Those are the 65% of people who actually fill out the forms and mail them back. And those forms are a lot of work, so accuracy is a whole other issue (Visa would probably be better equipped than the BLS to determine inflation). And if wealth inequality increases and inflation also increases (but money is moving into items that the middle class no longer can afford), that will not be reflected in the survey. The opposite is also true, but wealth inequality hasn't decreased much during the CPI's history. If wealth inequality remains constant, I would say CPI is not a "load of crap." Hyperbole, sure. But when so much is at stake, its nontrivial shortcomings do demand a bit of emphasis.
[0] https://en.wikipedia.org/wiki/United_States_Consumer_Price_I... [1] https://en.wikipedia.org/wiki/Consumer_Expenditure_Survey