It pops up the first two times you go to a domain or a URL that has mentions, so it should stop bothering you after a little bit of usage. I do hear you though, several people brought this up. The problem with making it a button is that people forget to click it (me included), and most of the interesting connections go unnoticed this way. If you have ideas how to make this better, please tell me!
How about opt-out instead. A button to disable it on a domain. Its very non-intrusive otherwise but I'd still like the option to disable thing. (I also sent this suggestion as a note from the bottom of the extension)
As I said in email, you only see the sidebar two times per domain (unless there are mentions of the particular URL you are on, then two times on that URL). You can also disable ampie on a domain completely by going into settings: click on the ampie icon in the extension toolbar, and you can add blocked domains there. URLs from those domains won't get sent to the server to be checked, and the sidebar won't pop up.
One thing that comes to mind is an option to toggle it to operate either in "always-on sidebar" or "on-demand plugin button" mode.
To riff on what metabeard suggested, another configuration option that could be presented to the user might be something like "domain-specific preferences for always-on or on-demand" so that certain websites are always excluded/always excluded.
