A. If time travel is possible, why has no one from the future ever come back and told us? People act like it's only a matter of time until scientists figure it out, but flash forward 200 years to when they have supposedly figured it out, why haven't any of those people come back and visited us in the past 100 years - have you, your parents, or your grandparents ever heard about or met anyone from the future? Perhaps it's not invented for another 1000 years and maybe they don't consider any of the last 100 years to be interesting enough to waste 2 time machine tokens on, I don't really know. I don't think time travel is possible.
B. I suppose that a better question is do you think it's plausible that there are multiple time lines running at once? In other words, are our past-selves and future-selves living out their lives at the same time we are experiencing it or is time more of a one way street? Once something has happened, you can't go back. And something that hasn't happened yet, can still be determined with infinite outcomes. That's really my main problem with time travel - it suggests some sort of pre-destination to our actions. I hate the thought that I don't control my own destiny.
C. Time Travel Paradox: If time travel were possible, and you went back to the past and killed your parents before they had you, what would happen? Would you cease to exist and just disappear? But if your parents died before ever having you, then you were never born. If you were never born then how did you travel back in time to kill your parents?