Yes, the folk that make up the majority love Garnett. Have you ever heard a negative word about Garnett from ESPN, TNT or NBA TV? He's had a positive reputation since the Minny days. His antics have always been looked upon as playing hard and being savvy/a veteran playing mind games.
Yes, the Celtics are a defensive team and rely on consistency on that end. When it comes to importance, a 26 yr old Rondo is more important to the Celtics than a 36 yr old Garnett who it wasn't sure was even returning to the team this season when they got bounced last season. Garnett brings a lot to the table defensively as far as leadership and on court performance, but defense is the philosophy under Rivers regardless of Garnett's presence or not. Who is going to run that offense if you take Rondo out? They lose a ton if you take either away, but the loss of Rondo would be more detrimental imo.