I think people will chill out over time about this. Counsell was a likable presence and a solid enough manager, but (1) he is not some sort of managerial savant, and most of the posts on here during games were rightfully complaining about his poor decisionmaking and roster management, and (2) he spent most of his career elsewhere and only spent a few seasons on the Brewers at the tail end of his career. I vaguely remember knowing that he was from Whitefish Bay during his time here as a player, and it became a nice story when he returned to his hometown team as a manager, but minus that "nice story" I doubt people would even care about this at all.
It's very different from a hometown player leaving during free agency, and it would be very different if this was Robin Yount or someone who was an iconic Brewer mainstay. Counsell has a nice run here as manager, but if anything we have underperformed from the level of talent on the roster despite making the playoffs regularly. I don't care that he's leaving for a rival. I will barely remember he's there just like I barely remembered that David Ross was the manager.