When you say they're running through a map, are you on the same Fireteam? If so, that's a little rude by them but perhaps they've seen that same level or Strike possibly 20 times already and are speed-running it. If you're out on Patrol...well then others are free to do as they please, though I'm sure that's not the case. Typically, I go through a mission with a Fireteam at the pace we set each other. If someone is lagging behind, then I typically slow the pace a little until everyone catches up.