Aether was protecting itself by attacking Earth police, Asgardian guards who were touching Jane. Why didn't it attack Thor & Odin when they touch her?
I'm not so certain it was the Aether protecting itself.
- It was bonded to Jane in a way the Asgardians couldn't undo.
- As far as I recall, for the most part it didn't attack those that Jane didn't want hurt unless they surprised her.
- The visuals during when Malekith bonds with it were not that different than when Jane did.
- Malekith was able to control the Aether while bonded to it.
It looks to me like the Aether isn't sentient, it just reacts to its host's thoughts - a small instinct like flinching or just plain dislike of cops would have been enough to trigger it.
A number of things could have made it seem random/semi-sentient: Jane not knowing how to control it, or humans not being very compatible, or because the bonding wasn't complete.
They also say the Aether woke the dark elves up before it had a host at all, and it stretches plausibility that of all the people that could have found it Jane just randomly stumbled on it.
Seems to be able to manipulate things around it to get to the host it wants to be in, at least by implication so it's unlikely just mirroring it hosts thoughts.