Agreed. And doesn't every fan have the right to complain? I'm up on the fence on the whole McD issue right now, but there was a time when I was firmly against him continuing to coach here. That isn't the issue though.
If the email really was from JP, IMO it was a flippantly arrogant email that should really have been thought through more carefully before being sent. If not from JP, whatever media/comm. person sent it needs at the very least to have a stern talking to. With the current campaign to increase the number of donors starting up, right now is not the time for those type of emails. Also with a team that performed as poorly as ours, he should expect some negativity. Honestly, even if the team got to the national championship game and lost there would still be some calling for a new coach.
Your point about dissuading potential fans is really the one I would like to speak about. Even if he hasn't bought a ticket (or has only bought one), that still isn't a good reason to talk to him like that. I'm getting to the end of my fifth year here and getting ready to graduate, but in all my time at this school, only once did I ever have to buy a season ticket. Granted, this is because I was in band and got to go to everything for free (if you don't count the 600 or so dollars each year that taking the 'class' for band costs) but I still went to everything that I could. Perhaps the writer of the email was in a similar situation or was a cheerleader or something of that sort. Anyway I digress.
The point is that I am very shortly going to be graduating and my income will be increasing immensely. I am faced right now with the choice of how to spend that money, donating it to athletics and buying tickets, or not (of course if I am anywhere within 500 miles I would buy tickets, but the way things are looking, I will probably be in Louisiana either for work or grad school at LSU.) I'm sure though that there are many like me who will soon face the choice of buying tickets and/or donating to athletics for the first time. You really don't want to do anything to convince them that the athletics program is not where they want to be putting their money.