OP I suspect you're not a committee member for your local WI?
I have been on a committee for another volunteer-run organisation and in my experience, most members have no idea at all of the input that goes on behind the scenes so that you can have your weekly/fortnightly/monthly meetings. Many of these volunteers also have very full lives, possibly work, childcare, caring for relatives. Thinking of the traditional demographic of the WI I suspect many may have been shielding, and probably struggling practically and emotionally over the last few months.
I also understand the GDPR issue, having been on the shitty end of fraud myself.
But we are all working in whatever way in a new world, and adapting meetings online (again, the demographic of WI suggests a group of potential 'silver surfers, struggling with new technology, but I know that many folk have utterly embraced the new-fangled technology 
).
If you consider this to be such a severe breach (I mean, it is a breach if your information was shared unnecessarily, but you haven't given any context for your rather extreme reaction) then why don't you volunteer to become the data protection officer on the committee? That way you can ensure all members and volunteers are aware of the GDPR responsibilities and implications.
Or you could just leave it to the obviously incompetent volunteers that don't care about data protection and shouldn't be trying to keep your WI afloat, providing support for all the members during what has been an unprecedented time 