Inflammation can be good or bad.

You really don't want a section of a nerve to be inflamed because the body is attacking the coating, for example. You do, however, want the skin surrounding the scratch on your leg to have some inflammation to help close the cut.

None of this means you should regularly take an anti-inflammatory drug nor does it mean that an "anti-inflammatory" diet or other preventative measures will help, either. I view some of this as the latest pseudo-science, at least in the hands of most folks.

This is slightly incorrect, because inflammation is not only triggered by "diseases". Inflammation indeed hurts the body. Some of the weapons it deploys, for example Neutrophil extracellular traps (basically, playing Spider Man with webs of DNA) make subsequent cadiovascular disease more likely. Others are just generally bad for the body or uncomfortable (fever, ratches, ulcers).

Chronic systemic inflammation is known to play a role in the development and progression of coronary heart disease and diabetes, and accelerate the transformation of the immune system into an aged state, which makes it more likely to develop immune system disregulations such as autoimmune diseases, and to cause cytokine storms when exposed to agents such a N1H1, Epstein-Barr or Covid.

The immune system consists of many moving parts coordinating each other via the exchange of signalling molecules, which results in a large distributed system with lots of unintuitive emergent behaviors. We are only just starting to understand what effects our everyday behavior has on the immune system, and what happens to it when we age.

It might also be the body's natural response to a poor diet, or carrying too much weight.

Yes, you're more vulnerable to disease when you are living an unhealthy lifestyle. Shocker.

Please define "unhealthy". This is a higly ambiguous term, and its definition differs a lot between cultures and across time, therefore it is far from obvious what living an unhealthy lifestyle means.