You will want to have image stabilisation when at longer focal length as it not only helps in capturing a stable shot but also aid in composing the photo by reducing the shakiness, thus giving you a more accurate handheld framing.
Image stabilisation is also good when you do not have a tripod but you want to drag the shutter speed for a mood shot. I.e a still subject but with motion blurred background.
There's a whole army of photographers (on this forum and elsewhere) who were producing good work before image/lens stabilisation was ever introduced. So 'no', not strictly 'necessary'.
In the same vein, all you really need is a sensor, lens, and shutter (+ some control device/circuitry) in a light-tight box. You don't NEED a LCD display, auto-aperture, autofocus, auto exposure, in-finder displays, etc.
Like all these other features technology has added to our tools, it can be very useful. And it can open up new possibilities and opportunities that just didn't exist before.
Use what helps you to get the results that you want / need to deliver. If you have always bright sunshine and can use ISO 800 then there is little need for additional stabilization. Maybe you should try your lenses on the long end after sunset, somewhere in the city, using ISO 800 as maximum value? Of course, no tripod