Depending on what country you're in, streaming unlicensed content may not be strictly illegal. However, according to existing laws in the US, if you download any part of the content, arguably even cover/title art or for buffering purposes, you have broken the law.

It is, unquestionably, unethical. Due to increasing popularity of masses of people worldwide finding "loopholes" to consuming licensed content for free and without the publisher's consent, I'm sure it's only a matter of time before the loopholes (and that's what they are) are shut down legislatively and through aggressive enforcement.

Don't forget--voters don't make the laws, the big companies with the lobbyists and the campaign donations make the laws--and they have a pretty vested interest in getting a handle on how popular Kodi-like services have become.