The bacteria which causes Botulism is not killed at boiling water temperature ... so if the bacteria gets into during the process of canning beets or any low acid fruit or vegetable, it will form the toxin which will then cause botulism. In days gone by with the water bath canning that went on a few people did die from eating contaminated jars of food. Botulism is nearly always fatal ego the only way to avoid it when eating canned food is to can the food properly so that the bacteria is killed during the processing.
Or you can take your chances ...