I don’t support this idea because of two reasons:
1. People would regret it after a while
I think that the chances that people accidentally unfriend all their friends is too high.
I also think that some people aren’t always aware of the action and that it couldn’t be undone.
2. This function is not regularly required
I don’t think that there are many people who need to unfriend all their friends multiple times.
Conclusion
I would prefer a faster way like you already suggested in another topic because I think there will be too much accidentally ‘unfriend all’ action.
This feature would fit better in the Following tab, because there isn’t an amount on people which you can follow so I think that there would be more demand for a feature to clean them up on a fast way.