I don't think it is a matter of belief, but what science has shown us.
Type 1 diabetes is genetic but type 2 is much more complex.
Genetically you can have a higher risk, in other words you are more insulin sensitive. This is similar to those people who are at a higher risk for skin cancer than others. Does this mean they will get skin cancer even if they stay out of the sun? Of course not.
If you are more insulin sensitive than others, you need to watch your carb intake more seriously. type 2 diabetes is not genetic in almost all cases, and can be prevented. Not only can it be prevented, but it can even be reversed in many cases.
No medication is needed if someone eats correctly. Of course most people wouldn't know this since billions of dollars are made off people buying these products.