Very neat idea.

But I worry that it's vulnerable to bad people.

Got a hefty personal bill coming up, and you're pretty confident your SaaS business will be dead within 6 months but Stripe has no way of knowing based on current numbers?

Thinking of getting a divorce (startup or marital)... maybe time to grab the largest advance possible before your soon-to-be ex(-co-founder) realises?

The problem is that even if only 1% of Stripe's customers might match these kinds of profiles, that same 1% might be taking 20% of the Stripe Capital advances.