What do you mean? I can turn javascript off in my browser which effectively takes control of the front end by preventing communication with the server. Native is a different story but saying "there's no such thing as a front-end that you control," is misleading.
Did you write the browser yourself? On an operating machine that you hand-coded on a CPU architecture that you clean-room designed and implemented personally?
I even soldered the cpu
I smelted my own silicon
How do you know the silicon in the Matrix was not back-doored?