To tell or not to tell...really is a very personal decision. In my case, I was never in any doubt that I would tell anyone who asked or if it came up naturally in conversation.
I may be in a different position from many because while in my 20s I lost over 125 lbs, and kept them off for over a decade, until my thyroid retired (it decided to stop working) in my late 30s. So, I have lost weight the "right" way, and been successful over the long-term. When my weight started to increase, I returned to what had worked for me in my 20s, and IT DID NOT WORK. It was then that I began the very damaging cycle of trying every diet under the sun, losing about 20 lbs, then regaining that and more. I made a well considered decision to have VSG because despite my prior experience and success with significant weight loss, it became apparent that my body was very different now, and I needed to find an alternative that worked.
I listen to those who want to share are their WLS horror stories, and then simply state that everyone's experience is different, and then move on. In my experience most people have been either neutral or supportive, but then I don't give anyone much opportunity to "bring me down" with anecdotes or uninformed opinions. I've done my research, and I'm secure in the decision I've made for myself. I am not ashamed of my decision, and I refuse to accept any stigma that others may want to attach to WLS.
Everyone has different life experiences, and so they will come to different conclusions about what is best for them. My perspective is that each decision is valid, and no one should feel pressured, either to tell or to not tell others about their surgery. If you are at peace with your decision, it is the right one for you, and that should be all that matters.