From the official GrapheneOS response to exactly this same debate, it seems that the issue is MicroG's reliance on having signature spoofing enabled. Which is a security hole that can be exploited by anyone, not just MicroG, as it allows anything to masquerade as Google Play Services to an app that wants to use it.
Yes, Google Play Services is closed source and contains functionality that would be considered "spying on the user", and "malicious". But that is the same for any closed source app; you can't prove it isn't trying to spy on you or compromise your device. What you can do is rely on the App sandboxing and fine grained permissions control that GrapheneOS allows to disable such functionality if it exists.
Of course, if even having a closed source app on your device is too much, then honestly you wouldn't even be using MicroG as you wouldn't want any apps using Google's proprietary libraries for accessing Firebase or other proprietary services anyways...
So, GrapheneOS offers the most sane approach in my opinion, without opening any security holes. By default the entire OS (not talking about pixel firmware blobs, just the os and kernel drivers) are open source and you can use only open source Apps via Fdroid, Accrescent, direct with Obtainium, etc. But for the average user enabling sandboxed Google play and managing its permissions is the best compromise between security and privacy.
Spent 4 hours on Sunday debugging "SW microcode error" iwlwifi crashes... eventually found some random shit on the Arch forums where you turn a bunch of shit off and it fixes it
From the official GrapheneOS response to exactly this same debate, it seems that the issue is MicroG's reliance on having signature spoofing enabled. Which is a security hole that can be exploited by anyone, not just MicroG, as it allows anything to masquerade as Google Play Services to an app that wants to use it.
https://discuss.grapheneos.org/d/4290-sandboxed-microg/11
Yes, Google Play Services is closed source and contains functionality that would be considered "spying on the user", and "malicious". But that is the same for any closed source app; you can't prove it isn't trying to spy on you or compromise your device. What you can do is rely on the App sandboxing and fine grained permissions control that GrapheneOS allows to disable such functionality if it exists.
Of course, if even having a closed source app on your device is too much, then honestly you wouldn't even be using MicroG as you wouldn't want any apps using Google's proprietary libraries for accessing Firebase or other proprietary services anyways...
So, GrapheneOS offers the most sane approach in my opinion, without opening any security holes. By default the entire OS (not talking about pixel firmware blobs, just the os and kernel drivers) are open source and you can use only open source Apps via Fdroid, Accrescent, direct with Obtainium, etc. But for the average user enabling sandboxed Google play and managing its permissions is the best compromise between security and privacy.