Generally speaking, most rattlesnakes are not protected by law from killing in a humane manner. There are, however, some species that are protected because they are rare or endangered. While these species are not to be killed, often it can be worked out with wildlife authorities to live catch and transport to other areas.
The clearing of a site for a restaurant means that the snakes were not living with people, but people were trying to live with snakes. The situation as described is not one where snakes were found in someone's home or barn, but where humans encroached on the snake's territory. The snakes apparently were not a threat until disturbed. So, you call in Fish and Wildlife and let them do their thing and everyone goes away happy, including the snakes.
Keep in mind, most rattlesnakes enjoy dining on small mammals, most notably rodents that humans despise. Rattlesnakes usually do not attack humans unless humans have done something to the snakes such as step on them, try to catch them, or interrupt mating rituals. Snakes have a bad reputation that really is not deserved. Additionally, rattlesnake bites are rarely lethal except to smaller animals, children, or the sickly or very elderly. Copperhead/moccasin (rattlesnake cousins) bites are almost never fatal because they physically lack the ability to store enough venom to affect adult humans.
So the statement that "rattle snakes are more important than peoples' lives" is somewhat naive since rattlesnakes are not the great predatory human killers people make them out to be.
Chances are, if you heard rattlesnakes can't be killed because it is against the law, it was likely bulls*** unless the snakes were rare or endangered.