You can also rhetorically ask them what is true loyalty and follow up with an illustration/parable:
"A certain man named Peter had two friends, Mike and John. Whatever the Peter does Mike always supports him and he never ever tells Peter he is wrong even when he is clearly going the wrong way. But John will point out to Peter if he is going wrong because he does not want Peter to get into difficulties with the law. Which of these two men seems to you to be truly loyal to Peter - Mike who always agrees with everything Peter says and does; or John who would bravely offer him corrective advice and criticism when he's going down the wrong path?"
You can use this illustration to say that blindly going along with any and everything the uninspired and imperfect governing body teaches and does, is not true loyalty and that one who is truly loyal will bravely speak out about wrongs and errors so that they are corrected so that the slave does not end up being judged as the evil slave when Jesus returns. But if the slave is silencing all constructive criticism and wants total unconditional loyalty, then how do we know they're aren't already the evil slave?