It sounds like a good idea, if you have the time+skill+money to do it.
Odds are that your instance won't be big. But at the same time, you'd have an easier time moderating it, specially if you only federate it with "cleaner" instances. (With "cleaner" meaning "that don't post content you'd remove").
*rolls eyes* "Great".
I might be wrong, but I think this whole issue boils down to four vices brought from Reddit: assumptions, decontextualisation, genetic fallacy, oversimplification. Those four on their own already make social media hostile, but if you couple them with political engagement (otherwise a great thing), you'll get people who genuinely see no difference between "they euthanised a 11yo dog with cancer" and "they kill puppies".
Or between "free Luigi" and "
$CEO_name
needs a Luigi in their life". Both show support to the same cause, but only the later can be reasonably understood as a call to violence (to the point it'd bring the admin troubles.)