Geez, that’s a good question.
I’ll bet you didn’t know that each LEGO piece is manufactured to an exacting degree of precision. When two pieces are engaged they fit firmly, yet can be easily disassembled. The machines that manufacture LEGO bricks have tolerances as small as 10 micrometers.
Despite variation in the design and the purposes of individual pieces over the years, each piece remains compatible in some way with existing pieces. This means that LEGO bricks made in 1958 still interlock with those made today.
With this kind of precision, LEGO pieces will stick together without using any kind of adhesive. If you get creative with your building techniques, your MOC will have a stable construction using just the interlocking studs and tube in the LEGO bricks.
Plus, LEGO pieces are meant to be combined in any way that the builder can imagine. Just sixe pieces of 2×4 bricks can be combined in 915,103,765 ways. If you glue the bricks of your MOC, you won’t be able to use any of those pieces in other builds.
So to answer your question, no one can prevent you from using glue in your MOC. However, OhioLUG members challenge each other to refrain from the practice and the amazing creations displayed by OhioLUG members do not use any type of adhesive.
Thanks for writing,
Your friend Emmet