It's only secret-from-your-friends. Actually, secret from your friends if they can't identify your writing style and personal idiosincrasies, and if your friends don't happen to include people in the SF startup scene that are friends with anyone at Secret Inc.

Hi, I'm one of the founders. We ask for your phone number to connect you with your friends. We also encrypt unique identifiers so that your friends, nor us, can ever read your content.

Read about our stance on using address books here: https://medium.com/tech-talk/4791cf1fcf0e

I would say they lost me even before that, the website won't even load without javascript.

Besides if they can't even have a website that are not tracking me and sharing my info with 3d parties (i.e. Google-analytics, Cloudfont, and Amazon Web Services), how could I ever trust their product/app?

You don't need to give it, it's just an easy way to deliver it to your phone.