How to open nautilus without a desktop?

Run gsettings set org.gnome.desktop.background show-desktop-icons false and Nautilus will always start without drawing the icons on the background.

You can also run dconf-editor to change the setting with a GUI, if you'd like.

You may need to reset your background image settings, depending on how well the system handles the nautilus background window disappearing.

Execute nautilus with:

nautilus --no-desktop &

You can change the launcher accordingly or create a new one for your purpose.

Edit: Added ampersand so that the process is run in the background. (Props to @user117123)