Cwatters illustrates the stall/spin problem with model flyers who focus on ground speed instead of airspeed. Imagine what would happen to the glider if the pilot DID try to make the ground track circular? If there was a good wind, he might stall/spin on the downwind-to-upwind turn in the thermal.
The glider tug pilot who wants to make a left downwind turn after taking off with a right crosswind, should first turn right to negate the sideslip, then perform a balanced turn to the left. It will take longer to get to the desired heading, but at least you'd arrive at the final heading with normal airspeed. However, if the tug pilot insists on maintaining a ground track (AND heading) along the extended centerline of the runway, he will be in a right sideslip due to the crosswind just prior to making the left turn. If he turns left now, he will experience a loss of airspeed because the turn is not balanced.