Chess is not a sport, it's largely a prearranged game, all of the end games and all of the openings have already been completely worked out for you, it's just a matter of studying them, it's only the middle game that can claim any kind of creativity but even then a computer can work out the best move, you cannot use a computer to determine the outcome of real sports that actually involve physical exertion and split second decision making. This is not even a debate, it's laughable nerds and geeks are trying to make out they're sportsman
You can talk about this all day long every day, but the vast majority of people are never going to accept sitting on your arse, hitting a clock and moving pieces of wood is a sport. Get over it.
1) it's a relatively meaningless semantic argument that in my experience boils down to: "but the thing I do / like is hard / tough / to be given respect too!"
2) if the point is to prove that chess is hard / tough / to be respected for the effort involved, it's an uphill battle to compare it to 'sport' in terms of how gruelling it is. You're accepting the bait and arguing on their territory. Talk about mental toughness and processing speed, etc - that's the bit that 'sport fans' see as elite and chess players are best at. Anyone's favourite athlete "sees the game differently", "has eyes in the back of their head", "is two steps ahead of everyone else", "is playing chess while everyone else is playing checkers", "is tough under pressure", "never gives up", etc.
3) For a group arguing about mental acuity, there sure are a lot of people backing up this argument from an early post:
"First and foremost, it is important to consider the definition of a sport. The Oxford Dictionary defines a sport as “an activity involving physical exertion and skill in which an individual or team competes against another or others for entertainment.” While chess may not involve physical exertion..."
Whatever arguments you want to make, that's not where to start.