Goals from Darren Potter and Daniel Powell handed the Dons a routine 2-0 opening-day victory at stadium:mk before Kay was sent off for his scuffle with Oldham striker Simpson.
"Simpson should have been sent off three or four minutes before," Robinson said. "He's punched out at Darren Potter in the back of the head.
"He's gone through the back of Luke Chadwick and he's jumped with his elbow into Antony Kay and cracked his nose. His nose is a mess, there's blood all over the place."
Robinson added: "I thought we looked very strong and very professional - we weren't as fluid as we always are but it was the first game.
"People keep telling me that it's one of the best Oldham teams they've seen for a long time so it's very pleasing for us that we can roll our sleeves up and fight like we did."
