Why is it necessary to have to purchase mandatory  basic insurance 645 baht when the vehicle already enjoys class 1 insurance, or am I being scammed at the annual test /road tax renewal?

Because it's the law.

 

Class 1 covering your vehicle & occupants is optional for your protection.  If you pay extra to extend coverage to others, that's also 'your' option.

34 minutes ago, KhunLA said:

Because it's the law.

 

Class 1 covering your vehicle & occupants is optional for your protection.  If you pay extra to extend coverage to others, that's also 'your' option.

Understood, but my class 1 way exceeds the basic compulsory, in the event of a bump who pays out the state compulsory or the purchased additional option?

If everyone acted responsible as yourself, then laws wouldn't be needed.

 

Unfortunately ... 

in case of injuries, your first class insurance would ask the party to make a claim from the mandatory insurance first, then anything above that they pay on top, so it's not like it don't get used