JustFly Momentu Ventures FlightHub Fined me for canceling reservation within 24 hours of original booking. Bellevue Washington

This is against the law, unethical, and unjust.

First off the regulation you talk about ONLY applies in the case where you book with the Airline directly. 3rd Party booking companies are not required to follow this regulation. So because you booked though a 3rd party site, you are subject to their terms.  This is another reason why you should ALWAYS book through the airline directly. 

There are also an additional items that the 24 Hour rule does NOT apply to flights departing within the next 7 days. It is also a strict 24 hour period. That is if you booked your flight at 5PM on Friday, and called to cancel at 5:15PM on Saturday you are outside of the 24 hours.

Now, when it comes to their terms. The time to complain about the ethics or how unjust it is, is BEFORE you purchase the tickets. As if you didn't agree with the terms which included any cancellation penalties, you should never had agreed to them and purchase the tickets. If you say you never read the terms then that is on you.