Purse was handed a red card 12 minutes from time, after tangling with Fleetwood's Jamie McGuire on the edge of the Argyle box.
Fletcher said: "I think Darren was sent off for a straight red, I've not seen it, but that's how I think it has gone.
"When you play a football match, every game is different and sometimes the will to win boils over into actions that you wouldn't normally do.
"I've done things on the pitch that in the cold light of day you wouldn't do and I think for people who haven't played it's difficult to understand the adrenaline, the frustration and that will to win.
"Sometimes you do things you wouldn't normally do."