Do all bacteria normally cause disease?

No. Bacteria are ubiquitous. Our skin is covered with bacteria and the lining of our gastrointestinal tract harbor numerous strains of bacteria that coexist peacefully with us, their hosts. Some of them actually help us with processes like digestion, and fighting infections. Only a fraction of bacteria that exist on earth are harmful to humans.
No. Many bacteria are completely benign, and we would have a great deal of trouble surviving without them. Our body literally is covered with bacteria, inside and out, with some important exceptions such as the bladder and internal organs. The gut is loaded with all sorts of bacteria that actually helps with digestion.