Explain to me like I’m 5, why this is a bad idea…

determine exactly what he is asking and then explain, in writing that you object because of risk. Then get it in writing that he understands, and wants you to proceed anyway. Tell him simply that this is because you'll do whatever you are paid to and that you don't want any negative impacts such as downtime to be blamed upon you and that this situation is well outside of your professional risk tolerance you apply consistently to the duties the organization has tasked you with. As far as how to have the conversation, you want to calmly ask how much downtime is justified, or how much re-tasking of your time is justified. You dont say it like that, thats just how I'm saying it here briefly to you. Be polite and political about it. And again, get it all in writing. Realistically in a best case you dont get your ego or emotions involved. You work smarter not harder by covering your ass. If the request is demonstrably absurd then may consider involving someone else, but you had better be right because if he wins their opinion and you are still told to do it anyway and there isn't downtime or noticeable labor cost then you will look like the bad guy. If shit hits the fan, you want a paper trail of you reasonably calmly and professionally informing your boss of the risks involved, reiterating, then double checking one last time prior to taking his ill-advised action. This sucks to have to admit this but realistically by professional IT standards you can disregard a lot and not necessarily impact a companys bottom line. For that reason you wanna be calm cool and collected with warnings and documentation thereof. Otherwise non-IT people will be very quick to label you as crying wolf and disregard your warnings even more. Do not forget, if the pain experienced isn't too directly correlated to the cause then the association is often lost. This can often by merely by time.