Banfur, the tire dealer is speaking the truth. However, us Jeepers are a little hard of hearing and slow in understanding. hehe...
Sure, the heavier tires are more stress on the suspension and drivetrain. That's why we do mods elsewhere (ball joints, driveshafts, gears, axles, etc.). But it is not like your Jeep is going to suddenly fall apart on the side of the highway someday.
Just understand that in addition to the lift kit and big tires, a lot more goes on to make our Jeeps trail-worthy. There is a lot of stuff you don't see at first glance when you look at a lifted Jeep.
Once you get your Jeep lifted and on bigger tires, you'll find a whole bucket load of reasons to further modify it. Some costmetic, some mechanical. It can become an expensive hobby, but it is also extremely satisfying and fun!
Read through those threads for a while and ask questions. Don't sweat it. I was in your shoes at one point, also. Figure out how you want to use your Jeep. Mine is built for rock crawling. If you are looking for great street manners and occasional off-roading, AEV makes a great lift kit for that. Their lower control arm drop brackets keep it feeling as close to stock as possible. However, you lose a couple of inches in ground clearance.
The one truth out there about Jeeps is: J.E.E.P = Just Empty Every Pocket
2008 2-dr Rubicon, auto,
RK 2.5" Max Travel, Rancho 9000XL shocks, 37" Nittos, 5.38's, RR skids, Warn VR8000-S.
RIPP Gen 2 Stg 2 Supercharger.
Political Correctness offends me.