So when making my space stories I have put them in a technological time in history where gravity manipulators are available to the common creature and you can use it to go to other planets and live in zero-G environments, the science isn't important(mostly because I'm shamelessly hand waving it with two words Exotic Matter) and what it exactly does is make the gravity a person(creature) experiences equal to that of their home planet, rather than that of their current environment. And this is a problem because it leaves the option for any person to use the gravity machine to experience less than their normal gravity, effectively giving them super strength, and this happening would mess up the story and plot as a major theme is natural ability of different creatures. So my question is what excuses or reasons could I give to why no one uses this technology like this?
Gravity changes weight but it doesn't change mass. You can't swing a 2 ton anime sword like a normal sword just because you're in zero G. It would be more like pushing a really heavy fridge around on wheels. Hard to start and hard to stop.
Changing gravity isn't really super strength. You can move heavy objects but only slowly and the heavier they are, the slower you can move them.
I'd rather an exoskeleton which would actually give me super strength.
Gravity weapons would be far different than plain old strength. If you reverse gravity, your enemy falls up or if you increase it, you squash them like a fly. If you use zero G, you stop them from fighting back easily.
Nobody messes with standard gravity because gravity isn't personal. If I reduce it for me, so that I am stronger relative to the massive objects around me, I am also reducing it for you and making you stronger. So instead of beating each other up with baseball bats, we swing automobiles at each other. (sort of reminds me of Superman vs General Zod in that old Christopher Reeves flick).
Since medical science is not enhanced by gravity manipulation, and since it is easier to reconstruct a skull that has been hit by a bat than one that has been hit by a bus...
Nobody messes with the gravity controls.
The sad answer to your question is "no", people will manipulate gravity machines for their own purposes, and if they think they can achieve a benefit (especially an unearned benefit) by using the gravity machine with little risk to themselves, then they will likely go for it.
You can see this with people using various tools and implements in ways they were never intended or designed to be used in order to commit crimes. This isn't even crimes of violence (that was settled by our distant hominid ancestors when they discovered rocks and long thigh bones amplified their strength), computer hacking and programming malware, phone "phreaking", counterfeiting books, money and luxury purses and other technological flim flammery have existed for a very long time.
Now why didn't I think of this sooner?
Gravity machines, especially ones powered by handwavium provide plenty of opportunities for characters to mess up with worldbuiding, once you start thinking through all the implications of this. As many people have mentioned, gravity does not change mass or inertia: you can easily be killed by a car drifting into you and crushing you against a wall in zero-g. Similarly, if the gravity effect can be focused as you imply in your description, then you could increase local gravity and stick a person to a wall or the floor while you go about your nefarious plan. Since gravity is thought to be the effect of bending space-time by mass, you also need to figure out where the mass or equivalent energy is coming from or going to, as well as issues like heat dissipation. In other words, manipulating gravity has very profound effects outside of making you feel lighter or heavier.
And of course, what happens when the bad guys have a falling out, or the good guys grab their own gravity machines to battle the bad guys? How do intersecting gravitational fields work in your world? Can you set them "out of phase" and neutralize another gravity projector? Would you create singularities and suddenly deal with miniature black holes rapidly radiating away their gravitational potential energy through Hawking Radiation and radiating Petawatts of energy in their final moments?
Micro black holes are very bad news
So perhaps you need to reign in your enthusiasm and carefully think through the logic of your worldbuilding. Gravity generators are likely to have far more interesting and profound ramifications than simply making you temporarily lighter or heavier.
I don't exactly know how the gravity manipulator would work, but I picture the following. There is the local gravitation field
F_L without the effect of the manipulator, provided by the planet and everything around the region. And then the gravity manipulator adds an additional local field
F_M to the original field, resulting in the effective field
F_L is the given -- it cannot be change. The only thing you can restrict is
F_M. I presume you want to preserve the directional freedom.
Therefore, you can limit (1) the maximum magnitude of the vectors in
F_M and (2) the precision of control -- i.e. the maximum rate of change of the directions and the magnitudes of the vectors.
Please note that the fields do not represent the forces themselves, but rather the gravitational potential. And I did not care about the "conservativeness" of the field in the illustration, but gravitational fields do have to be conservative.
You can make the use of the suits in such a manner (aka make your self super strong) similar to Gun usage in the USA (I'm not american so this could be 100% bs).
Anyone could use the suit in such a manner, but to do so would be criminal and also raises the issue of escalation, where someone else will turn down the gravity of their suit to be able to combat you. With wide enough spread and usage, as well as a high level of education and a strong morale compass, the users of such suits simply find no need or urge to use the suits in such a manner, and if they did, the other uses would be able to shut them down.
You could also throw in some past history of criminals using the suits as such and being shut down, or maybe the gravity goes -ve and tears them apart. Some horror stories to stop people from going to the extremes of the suits power.
Finally, you could have each suit linked to some central system, and differing amounts of gravity will require different amounts of authorization. Hence a person who wants to have super strength will need to seek approval before being able to access it. Of course you might have people in modified suits that circumnavigate the authorization issue, but you will always have criminals.