i need to justify why having two sidebars on the same side is wrong

background

i have a right sidebar and a left sidebar, both are shown all the time, the right sidebar purpose is to change the background in the middle editing frame by selecting one of the options in this bar, this is always shown, i was asked to add another sidebar on the right side that is going to be a text options toolbar, where you can change fonts, style, size, etc...

i dont want to show both at the same time i want to have only one selected because there is no live preview of this editing flow so i see no point on having them both shown besides the code is already done to have one, show it and hide it...

my question is

How can i justify my assumption that having both right sidebars shown at the same time is wrong or at least that is not a good practice or is it?

Am i on the right track by assuming that i should not show the user too many options at the same time if he is not focused on using them all?

thanks!