This question asked about how to do item duplication in Minecraft, which on most servers would probably be considered cheating. ... The examples given are unquestionably cheating, but may be OK depending on whether the game is competitive multiplayer or not.

Does duplicating count as cheating?

It depends, if it's in a legit multiplayer server and you know what you're doing, yes. Any other time, it doesn't really matter, but I never use glitches in single-player. Takes away the fun of it.

Can you get banned for duping in Minecraft?

If it's just a glitch within the game, no, you cannot get banned and if they think of it as an issue, it will get patched as soon as they can. Unless you're modding or putting something in the game yourself, you can't be banned for a bug that was missed by the creators.