With Better, we set up a Facebook page in order to reach people we would otherwise not be able to reach.
However, we also have a disclaimer in the form of a pinned post that states that we are using the platform under protest. In other words, that we realise that it is necessary for us to use this existing platform monopoly if we want to reach people and effect positive change today but that we do not approve of its business model or practices. (Read more about our approach in Spyware vs. Spyware.)
I suggest that we adopt a similar approach at DiEM25, alongside an active initiative to move us off of Facebook and onto our own communication platforms as much as possible while relegating our use of Facebook to a publish-only stream of news, etc., and links to our own forums to reach those people that we might not otherwise be able to reach in the short term. (We must also encourage them to join our platforms so we can, eventually – in the long term – migrate off of the platform monopolies completely.)
For a screenshot of the Better Facebook page disclaimer, see my Mastodon post (placing images on this forum is a nightmare): https://d25.community/@aral/16139