AntiCheat

Why is there an Anti-Cheat on the server?
The Anti-Cheat only attempts to control flight and speed. During August 2020 there was a trial with no anti-cheat on the server. The results were:

Note: As of 8/28/2020, a new AntiCheat has been put into the server. While this appears to be better than the last one, an unfortunate side effect is Anti-Hunger is detected by Speed. For the time being disable this hack.

Chunk Speed Loading

 * With flight and speed enabled, players can easily chunk speed load.
 * When one or more players are doing this CPU hits 100% and TPS tanks.
 * Once TPS tanks tick based activities like farming and fishing become laborious.
 * There are other methods of fast travel around the server, which don't involve loading every chunk along the way.
 * The challenge of overcoming spawn is no longer there for players with a hacked client.

PVP

 * Veteran players have described PVP with flight as not as much fun.

Value of Elytra

 * With flight enabled there is no need for and no value to Elytra.
 * Breaks the spirit of survival Minecraft.

Fly & Speed Kill The Server

 * 1) The compute cycles consumed by chunk speed loading directly impact the dollars and cents it costs to run the server.
 * 2) Farming, fishing etc are extremely tedious on a server running at, around or below 10 Ticks Per Second (TPS). It makes for a less functional server.
 * 3) As the server continues to grow the number of concurrent players only compound these issues.

Additional Reading
Along with this article, other articles on this topic:

Hacked Clients

Hacks