Sometimes it seems that Facebook is not aware of its public perception at all. There are already proven stories about how Facebook has been gathering more data than they claim and are using that data in a way that they could not wait (like using their added phone number for two factor security to sell ads). There are no comments that Facebook is spying on users and listening to conversations.
There is no indication of how Facebook would position the assistant, either in the Facebook application itself or more than an Alexa replacement in the Portal hardware (assuming the hardware line continues). It is also not clear how advanced Facebook is in the construction of the assistant or even where. You are getting the voice data you would need to build the speech recognition piece.
It is also not clear whether someone wants a voice assistant from Facebook or not. The portal cameras have been failed in all accounts. Facebook's last attempt to make an assistant with human power (M) also fail. If we add to this the general erosion or confidence in Facebook, it is difficult to imagine how the company can sell a product that really includes it at all times.