Sure, there is absolutely no upside for me personally to do this.

There are only downsides for me, but I think they are limited: - My router lets me set the bandwidth limits for the guest network. I set it to 10Mbps down/1Mbps up which is unnoticeable. - My ISP has no data caps. - The laws here are not draconian

It looks like this concept is super old: https://www.schneier.com/blog/archives/2008/01/my_open_wirel...

If you were a crook, would you use a random open wifi for your illegal stuff? Wouldn't you use Tor or some proxy on top of that?