If people can transact with the blockchain for less cost than what it takes to run the blockchain, you are set up for a tragedy of the commons situation. Eventually, in this scenario, useless or unwanted transactions (spam) will take over the network until the point of collapse.

https://www.khanacademy.org/economics-finance-domain/ap-microeconomics/ap-consumer-producer-surplus/ap-externalities-topic/v/tragedy-of-the-commons

HF 20 is a type of paywall - the more SP you have, the more useful your account is.. And at some point it will be vital for the continuation of the platform.