Well, it seems that you have a lack of knowledge about 3D glasses. So, as a matter of fact, 3d glasses are designed to give us the exciting effects of the movie, and with 3d glasses we could experience and lifelike visual effects and experience. And generally speaking, within the period of duration, 3d glasses could be reused more than once. They are not bad for your eyes as long as you could be used to them.
Well, generally speaking, 3d glasses can be reused, and it is safe to do that, so you do not need to worry about it at all. And you also should know that 3d glasses are designed for your eyes to achieve seeing a slightly different image, in which your brain then combines into a three dimensional picture. In common, different 3D displays achieve this in different ways. Nowadays, it is normal to wear 3d glasses when you watch some movie. If you have a pair of 3d glasses while watching 3d movie, it will make you feel that you are just in the real phenomenon. This can be attractive and amazing. And you do not need change your 3d glasses every time.
The 3D glasses can be reused for sure, and they are always reused in movie theater.
Actually, it's not healthy in hygiene.You have no idea if the glasses were used by someone got pink eyes, if so, you are very likely to get infection.
However you cannot avoid it, so you can just do some prevention, such as clean the glasses by a piece of cloth you brought yourself.
Washing your eyes after you wear reused glasses, and eye drops may also help.