D2 is a tool steel, not a carbon steel.
Carbon steels are very easy to work with and heat treat. They sharpen easily and have good overall performance. They also tend to be cheap. The downside is that they rust easily. Examples are Opinel carbon steel knives, Moras such as KJ Eriksson and Frost, and the classic KA-BAR. These steels are numbered 10XX.
Tool steels are non-stainless, just like carbon steel. They are generally much tougher. They use a letter/number naming system. Tool steels tend to be more expensive, but higher performance. Some rust *VERY* easily. Some, like D2, are near-stainless-steels and bridge the gap between tool steels and stainless steels in performance and rust resistance.
Stainless steels vary from soft steels with poor edge retention (420J2), to very hard steels that can hold an edge for a long time and can compeat with tool steels (S30V).
Stainless steels are good for small and medium size EDC knives as they resist rust and perform well when not too large. Tool steels and carbon steels (and softer, tougher stainless steels) are better for large knives as hard stainless steels can be too brittle for heavy chopping.
What steel is the best depends on the application. For a EDC folding knife, I want S30V (stainless) or D2 (A tool steel, but very similar to S30V in performance and stain resistance). For a camp knife, I want a tool steel, not S30V.
While carbon steel is easy for knife makers to work with and heat treat, stainless steel is very difficult.
A steel with more than 13% chromium is a stainless steel. Some stainless steels barely qualify, while some non-stainless steels barely don't qualify.