Wouldn't two people pulling in opposite directions generate more tension than one person pulling a rope with the end anchored? (Assuming all people are equal)
The anchor pulls on the rope too, that's what you have to remember. You can swap one person out for an anchor and the rope wouldn't "feel" any different, still 50 pounds of tension.
Or put it this way: when there's 50 pounds of tension, that means that there's fifty pounds of force at one end and fifty pounds of force at the other end. It doesn't matter whether that force comes from an anchor or from someone pulling. Or you could have a pulley with a fifty-pound weight at each end. Or a rope tied to the ceiling with fifty pounds at the other end.
(The simplification here is that the rope mass is negligible. In reality, the tension will vary across the rope's length.)
(Or put another way: if two people pull on a rope with 50 pounds of force, the tension is 50 pounds, not 100.)