1. I remember in one sci-fi story, which I totally have to look up the title of, a Genius caught his wife cheating with his co-worker. Instead of outright killing them, he travels back in time to kill the ancestors of his wife, and yet, his wife is still there. He goes back and kill various historical figure, and the present is unchange...except, he loses corporeality, at which point he runs into ANOTHER time traveler. He is told that that one can only travel back to one's personal past, and alter one's personal past, and therefore no time traveler can encounter one another until their personal past is completely destroyed. I recall the phrase spaghetti sauce being used.
2. Time Travel in Star Trek...generally accepted fanon(?) especially on the Q side...there are always alternate timelines. One can never prevent something in the past from happening, ONLY, create a new alternative timeline, and move there.
THEREFORE:
The past!Steve that is in 616 right now, is NOT from the past of 616, he's from a similar timeline, except quite possibly, in past!Steve's timeline/universe, there is no future yet! If past!Steve stays in the 616 present, it really shouldn't affect 616's past at all, or the universe of 616 would be different the moment Steve arrives (removing himself from its past).
There is still past!Steve from another universe shouldn't stay here, because one, he's not the Steve that Tony remembers, and two, while it won't hurt 616, it will hurt the universe of this past!Steve, and hey, that universe has its own Tony somewhere in the future if they were to go there.
Space Time Continum
2. Time Travel in Star Trek...generally accepted fanon(?) especially on the Q side...there are always alternate timelines. One can never prevent something in the past from happening, ONLY, create a new alternative timeline, and move there.
THEREFORE:
The past!Steve that is in 616 right now, is NOT from the past of 616, he's from a similar timeline, except quite possibly, in past!Steve's timeline/universe, there is no future yet! If past!Steve stays in the 616 present, it really shouldn't affect 616's past at all, or the universe of 616 would be different the moment Steve arrives (removing himself from its past).
There is still past!Steve from another universe shouldn't stay here, because one, he's not the Steve that Tony remembers, and two, while it won't hurt 616, it will hurt the universe of this past!Steve, and hey, that universe has its own Tony somewhere in the future if they were to go there.