There is/was nothing outrageous about antimatter except the name. They could have called them "complimentary particles" or something more tame sounding. All particles can interact with other particles and produce reaction products. There was nothing novel about that either. Just because the reaction products here happen to be only photons instead of a mixture of photons and other new particles isn't much of a leap in surprisingness. They already knew about mass defect and E=mc^2, so the idea of converting part of a particle's mass to photons was already established.
Indeed, the name and their use in sci-fi settings trips people up into thinking they are some weird theoretical construct.
Medical imaging is a place where positrons are used in everyday life. Specifically, PET imaging or positron emission tomography in which a tracer dye is injected into the body. The tracer is usually biologically active, so that it is taken up in different amounts by different tissues. The tracer emits positrons which annihilate when they meet an electron and produce gamma rays which are then used to image tissue.
