There are different types of index funds. There are market capitalization weighted index funds that fit your description of buying the entire market, but there

There are different types of index funds. There are market capitalization weighted index funds that fit your description of buying the entire market, but there are also small cap funds, sector funds, value funds, etc. You can avoid certain companies (e.g. FAANG stocks) by buying certain indexes (e.g. a value index).