I applaud the sentiment, but you need to be wary.
As someone who has experience of a thriving community being gutted by another one that grew out of what we were running, I would love to say that we should all work together, but there do need to be some regulations of what can, and cannot be done.
I will admit from the start that we were not doing the very best we could have done for our members (we were a small team and busy organising the details of a conference each year) but our goodwill was taken advantage of by some who used our channels to access members and even sponsors, then co-opt our events to promote their own community. We had no specific rules in place to differentiate between promotion of individuals (good), promotion of sponsors (good, but they paid for the privilege) and promotion of other communities that used our resources and gave little back.
When communities are too closely linked, you are assumed to be “the same” which can bring positives, but also distribute negative associations.
I would highly recommend doing some soul-searching to craft a policy statement that encourages cooperation, but allows those who run the community to decide if a specific group or message is actually not constructive, and therefore can be reasonably withheld.