https://lists.fedoraproject.org/archives/list/[email protected]/thread/55H3DT5CCL73HLMQJ6DK63KCAHZWO7SX/
However, we also want to ensure that the data we collect is meaningful, so gnome-initial-setup will default to displaying the toggle as enabled,even though the underlying setting will initially be disabled. (The underlying setting will not actually be enabled until the user finishes the privacy page, to ensure users have the opportunity to disable the setting before any data is uploaded.) This is to ensure the system is opt-out, not opt-in. This is essential because we know that opt-in metrics are not very useful. Few users would opt in, and these users would not be representative of Fedora users as a whole. We are not interested in opt-in metrics.
Essentially they're playing with words to say it's opt in but if you just click Next like most users will do, it'll be enabled. The developer openly admits few users would opt in and complains that it wouldn't be useful.
There's a discussion specifically about opt-in/opt-out on Fedora Discussion here. Per the Fedora Project Leader, "this is the first time we’re using Fedora Discussion as the main place for a Change Proposal discussion". Make your voice heard!