I was under the impression that the First Amendment means that the government can't arrest you for what you say, not that it lets you talk about whatever you like at a conference organized or supported by it. Nevertheless I understand the urge of those guys to have their voices/ideas heard.

For what it's worth, ADA has released this press statement [1]:

> As a 501(c)(3) organization, the ADA has safeguards in place to ensure that it complies with all IRS regulations. This includes maintaining a strictly nonpartisan environment at all organizational events and functions while engaging across party affiliations to advance our mission. We have always, and will continue to welcome scientific inquiry, respectful dialogue, and diverse perspectives in the pursuit of better outcomes for people living with diabetes and obesity.

[1]: https://diabetes.org/newsroom/press-releases/american-diabet...