1. No criticism. After a loss, just say "good game everyone."
2. A little frustration. "Ahhh, catch the ball." "Make the tackle." "Coach, don't run it up the middle again."
3. Critical of systemic performance. "He's missed 4 tackles in a row. He's not playing well" "Our 3rd and short performance is horrific, coaches really need to figure that out." "What's going on in this program?"
4. Calling for action. "Bench him." "We need a new DC, this obviously isn't working."
5. Getting personal. "Our QB is a dumb dumb. He's obviously not committed, doesn't watch game film." "This coach is stupid. Doesn't belong at this level."
Categories are obviously simplistic.
Which level are you good with? And maybe it's different for players and coaches.
I think most agree that getting personal (#5) is too far and not the best. People are going to have wildly different opinions on appropriateness of #1-4. My perception is that you are saying only #1, maybe #2 is appropriate. And that those that disagree are not only bad fans but are bad disciples of Christ.