Does Defensive Tactics fizzle if the Gladiator beast is booked?

I need help with Defensive tactics, ive been told that defensive tactics doesnt get its effect if the only gladiator beast monster i control is booked , althought i tell them that is whats required to be activated and that booking it doesnt matter, they still say i dont get the effect. Im confused, please help me with figuring it out.|||Having a face-up Gladiator Beast monster is only the activation requirement for Defensive Tactic to be activated in the first place. After its activated, nothing can stop it unless something negates its activation (i.e. Seven Tools of the Bandit) or negates its effect (i.e. Trap Stun). Book of Moon does neither of these.|||well i thought that if they where chained book to Defencive tactics then the last card in a chain activates first so book would activate first so there would not be a face up gladiator beast so u could not prove that it is a gladiator beast.


so it should fizzle