I can confirm that it's currently not possible to manage the WhatsApp subscription in bulk via the contacts overview. The WhatsApp opt-in status can be edited manually via the individual contact's record, as described in this help article.
I, however, understand your use case here so I'd recommend posting this request to our Ideas Forum. We use it to collect ideas on how we can improve the product for our customers. Product pays particular attention to the top voted ideas & takes them into consideration along with other feedback channels as well as their own vision to understand what features will be most valuable. Thank you!