The purpose a conference is to select works for inclusion in the citation record for a field. The conference presentations themselves are secondary to the proceedings of the conference. A good way to know you're looking at an scientific conference is to find the Program Committee, which is the group responsible for determining which papers will and won't be accepted. Most scientific conferences are defined by their Program Committee.
I can't find Lambdaconf's PC online. I assume it has one?
Lambdaconf is an industry event. It's a gathering of enthusiasts that is mostly commercial and social in nature. Its presentations will be cited online informally. Because many of them are presentations by the authors of open source functional programming software, the subjects of those presentations may even be cited formally --- but it's unlikely that any of the talks themselves will be.
If Lambdaconf were an academic conference, I would have different feelings about their pointed inclusion of a noisome white supremacist. But it isn't; it's fundamentally a commercial event. It can't hide behind "science".