So, a few things stand out to me here.
First, the information that you provided here is NOT available on the page you linked. The website is just a signup page that asks for (harvests) email addresses.
Second, the submission of email is NOT requested by the ACLU itself, but rather the host of the Mobilize site (MobilizeAmerica, Inc.).
MobilizeAmerica Inc is a PAC, with almost no history and very little funding. https://www.opensecrets.org/orgs/mobilizeamerica-inc/totals?id=D000092936
All in all, this "event" seems like a way to harvest email, rather than an actual public service. I mean, why do I need to sign up for a livestream for what could/should be a simple YouTube video that anyone can access? Why not just send me a PDF of the tips and tricks?
OP, I'm going to assume no malice on your part, but I can't in good faith encourage people to use this service or attend this virtual "rally" without a bit more information.