Imagine if a lone "tinkerer" fiddled around and accidentally came up with your Phaser III type weapon. The decisions that person would be faced with. What to do with that kind of power? If he/she presents it to the government, there is no question how it will be used, and it could actually threaten the continued existence of everyone on the planet. It could be kept secret, only to be given over to the government in a time of dire emergency- like an alien invasion. Or the inventor might decide to just take over the whole world. He/she would be as powerful as any two armies combined. Would the government make a deal. submit, surrender, fight to the bitter end? Hard to be a one person army, though. You have to sleep sometime. I think that's the main reason super heroes have to keep their identity a secret.
You make an excellent point about the unpredictability of the future. I remember when I first saw B&W TV. I had never seen a color movie. So, I thought it was like a "movie" right there in the home. I had to stand outside this person's house to watch it (she would not let kids inside, and yet, would let us watch the Lone Ranger and Roy Rodgers through an open window). I thought you would have to be very, very rich to afford a TV set. When I saw my first color TV, I was just astounded. I would not have ever believed such a thing possible (I was about 14 yrs. old). At the time, I never even allowed myself to dream of owning one for myself.
I saw the "fantasy" of cell phones (called car phones in those days) I was about 24. I boldly predicted they were pure fiction- that such a thing would never ever be possible - and I had a degree in metallurgy and was working on one in electronics at the time!
I used my first "computer” (it was only a sort of word processor) and took up half my office- and put out more heat than a floor furnace. I confidently predicted, the thing had some limited potential for keeping telephone listings- that would be all.
But, I absolutely believed we would see the end of highways- all people would get around in flying cars and jet packs by 1980! Highways would all become farm land or parks.
I thought we would have solved overpopulation and see the end of all starvation by 1985! I also was totally convinced all disease would be cured (except death - although I can not know what I thought would bring on death if all diseases were cured...

) by 1990.
I was an avid Sci-Fi fan. I loved all things "space", a devout "Trekkie". - now look at the world of human. In truth, it has not changed but very little since 1960. Disease is a marketable commodity for the drug and medical industry- who would have predicted that? Cars still use internal combustion engines as a rule and roll on rubber tires (same as when they first were invented 1in 1890). There is no new energy source- still the same old crude oil Drake first discovered in Pennsylvania. I thought everyone would have their own personal nuclear reactor in their home by now. I never counted on oil becoming so endangered by the nuclear power development they would assemble whole armies of misguided citizens to stamp it into extinction. I should have foreseen that- look what the canal boat men did to steam powered canal boats!