You've just quoted the reason why: it won't be the last crazy idea they may have. That's pretty much an absolute certainty. Even if you can convince them with

You've just quoted the reason why: it won't be the last crazy idea they may have. That's pretty much an absolute certainty. Even if you can convince them with reasonable arguments to accept a few point less uptime, you're going to be having the same kind of discussion many times after on different subjects. You have to be really, really sure you want and need this kind of client. Most of the time (around 100%...) they are more trouble than they are worth.