"Be bold" and "fake it till you make it" are good slogans, but there is always a gradient between boldness and reckless negligence. "Take calculated risks" just doesn't have the same ring to it.
If OP gets banned by Discord and Slack, their product is dead in the water and they'll have to deal with angry customers who paid for a service OP can no longer provide. This means if this really is a TOS violation, they'll either have to fly under the radar (which arguably failed when they hit HN front page) or they need to grow influential enough to enter negotiation with Slack and Discord to get a special deal.
while Airbnb and Stripe are independent. There won't be enough money to fight them (Slack/Discord) if it stated in their TOS that they can turn off their services.
Linen's situation is more like developing add-ons for Microsoft's Office until Microsoft decided to add features that does what your add-ons do for free.
Where can I read more about that? It sounds fascinating..
This might be of some interest
Airbnb started by spamming Craigslist with fake ads. Stripe started by accepting payments to a single bank account. Doing something shoddy/somewhat shady and not being afraid of the repercussions gets you ahead in startups.
So what if OP breaks someone's "TOS", by the time they notice or OP's product gets big enough too care, he will likely have sufficient enough capital to fight them off. If he never gets that big, more power to him for something that makes him some beer money.