ChristopheHumbert I understand the concern. Fundamentally, Guest access is a sophisticated feature because there are so many controls involved that can send the experience sideways. Nearly every one of those controls is found in a different layer of software increasing the difficulty for some customers to manage. Over time, we've made each of these controls enabled by default, except for this one in Teams.
To be absolutely clear, nothing changes if customers have customized this parameter in their tenant. For anyone who views the Guest access capability today and sees the setting as "On" or "Off" - nothing changes. The only change will be for customers who are showing "Service default". The intent of these communications is to ensure everyone is aware of this change and understands the steps needed to manage if necessary.
Appreciate sharing your feedback, thank you!!