What you're describing is essentially the bootstrapping paradox.
To use a gaming example, take the Song of Storms from Ocarina of Time. Link learns the song as an adult from someone who learned it from him as a child. You then go back and play the song to the person who teaches it to you later. Where's the origin of the song? Who wrote it? How does it exist? If you go to the future and learn something and then take it back to the past, the origin of the idea will be destroyed. Depending on which set of the rules the Universe follows, that information will either be erased from your mind, since it could never have been learned, or it won't since you already know it and it's logically consistent. There's no way to know which ruleset is employed, since we can't test.
Physical objects, however, that are trapped in a bootstrapping paradox are much more complicated to think about due to entropy. If I find a jar and then take it back in time and leave it somewhere that my future self will eventually find and take back in time again, then that jar is in a loop. The loop should happen eternally, but the jar can't last that long. Eventually the jar will degrade to dust due to wear and tear, and the loop will be broken. Technically, from my point of view, that would happen instantly. Time loops involving physical objects can't occur from a perspective we'd find useful because the instant that one could happen it would stop and an entirely different set of circumstances would begin to unfold.
From a moral standpoint, I don't see the problem with stealing ideas from the future. I don't even think it would be possible to do so successfully. If you succeed in stealing it, the timeline prevents it from ever existing so you would forget it, but when you forget it the original creator will still create it, making it so that you can steal it again. If you don't succeed, then you get stuck in an endless loop of trying to steal it without knowing that you always fail, since the original inventor never loses the idea.
Causality is some timey-wimey shit.