Well, Texan fans are just naturally confident. That happens when your team never loses an opening game.
Believe me, you don't have to remind Texans fans about the 1st loss in team history. I pretty sure David Carr remembers being sacked 9 times in the 2nd game in franchise history. Don't expect that the Chargers will walk into the loudest stadium in the NFL with warm applause. Take a pound of flesh, you owe a pound of flesh.
As far as the logic used to explain why the Chargers should win, I'm not following you. The Chargers defense used to be good, now it's not. The team used to be average, now it's not. The Chargers had injuries and...wait, hold it right there. The 2nd year Texans led the NFL in players on IR in '03. And they still had a better record than the Chargers. You can't play the injury card here in Houston, my friend.
Look I respect Tomlinson, he's a great back. Considering the lack of talent around him, his production is legendary. I respect Marty, Wade, and the Chargers coaching staff. Given the time and the talent, I think they'll turn this team around. I don't think they'll get the time, but that's for another time & another thread. The Chargers are rebuilding, just as the Texans have been building for the past 2 seasons. The Texans are just a year or so ahead of the curve than the Chargers are. The Chargers have maybe 3 players on defense, and only 1 player on offense that would start on this Texan team.
Homefield, motivation, talent...the Texans have the edge. I believe in the adage "On any given Sunday..." Just not this Sunday.