Nobody should expect to be able to show up to every single spawn...though at the same time it is not unreasonable for people to expect a bit of good sportsmanship. Players who actively mess with spawn trackers are especially worthy of contempt. It may not technically be illegal but a lot of players put an immense amount of effort into spawning certain S ranks and it's utterly unfair to make it more difficult for them to keep track of which are available at the time.