I tend to be a 'it's the preseason' guy. I'm not saying I wouldn't rather we look awesome at all times. I just don't think fans realize how coaches generally approach these games. It's not to win. There is no gameplanning. It's not to have players doing things they know they can do. It's trying to determine a final few roster spots or find key backups. And they will often put guys into situations they arent comfortable with to see how they can handle them.
I do think fans *know* this - but we still tend to react as if we don't when it comes to reacting to the results.
On the penalties and mistakes, I don't see them as any different from other criticisms. The guys playing have had far less attention and practice time than starters and key backups. So I am not surprised that sitting 30 players we saw a lot of unforced errors.
Some teams in the NFL will have slow starts. It's just the nature of things. Some teams will win the first few games, some will lose the first few games. Chances are, very few NFL teams give their starters significant preseason playing time. I think there are 100 reasons why the teams that 'start slow' that are more impactful than preseason playing time.