Well I will answer it seriously first. Obviously time travel is not possible right now. If we were talking at least 50-100yrs in the future than I would hope culture would be different.

IF the culture was the same in the future if this was possible OR it was available now I think it would be made illegal due to the rationale of antis and it is this: kids are unable to consent without being manipulated in some way. They would say that you as an adult as smart enough to manipulate your younger self into having sex with you. Heck they would say that you would be even better at doing it since you would (he he) know him so well. ie you would be really good at grooming him, to use their terminology.

Now given this hypothetical situation an interesting scenario would be if you got caught in the past having sex with your younger self. If you could not then immediately go back to the future (depending on how this device worked) how would this work. How would you convince people who you were? If you could would it make a difference (what I said above)? Would the first BL to get caught get away with it since there is no law specifically against but any BLs after that would not? Just go back farther in time before that law is passed if possible? If you are a BL and can go back in time why not go back to when BL was more accepted?

This would be interesting for a moral scenario in general. Lots of movies, books, etc have tried to deal with the morality or time travel and how it would work, not technically but the problem of paradox.

Gs