THere is a lot to be said for a community having certain standards of kashrus for its local restaurants and supermarkets, and those standards being enforced by a vaad of local rabbonim having exclusive authority to grant hashgachos. Hashgachos also cost money to supervise; there are administrative costs in addition to the actual cost of the mashgiach’s salary. A communal vaad hakashrus thus has to charge for its services, and a business owner needs to anticipate and consider those costs before deciding to open a restaurant.
That said, you’re right. There is NO EXCUSE for a vaad to act like a mafia by extorting inordinate sums of protection money from store owners. A vaad needs to be responsible to the community, and if it acts inappropriately, the members of the community ought to replace the vaad members.