I get that you don't trust Amazon, but if you think they would protect your data less rigorously than Slack you really need to provide a more substantive argument.
Truth be told I love Amazon for the innovation they've brought to most of the industries they've touched but it's like there's some aura of trust around them just because they have brought some of their might against Facebook and Google which seem to be considered the evil twins on HN.
What's wrong with that? I feel like they've earned a measure of trust. Sure, they're not perfect but no one is.