Companies that buy advertising at games pay a pretty penny for it. Fans who buy tickets to games have paid to watch the game, not to advertise their cause. If fans want to advertise at games, they can pay the advertising rate.
Yes we must respect our corporate overlords, by their good graces we sit in their stadiums. It would be disrespectful to treat this private space like a public forum in any way. Even if the stadium WAS partially built using public funds...
Companies that buy advertising at games pay a pretty penny for it. Fans who buy tickets to games have paid to watch the game, not to advertise their cause. If fans want to advertise at games, they can pay the advertising rate.