It's not about what these guys have. They're letting you know (mostly through experience) that having 18's on a civic is not worth it.
Though at first you might think that it's the best thing that you'll ever get for your car, the longer you ride on them, the more you'll realize what a mistake it is to have such large wheels/tires on your car.
If you're at least going for the aesthetic aspect of such a large wheel/tire combo, might I ask if you have at least a body kit on your car (installed and painted)? Personally, 18's look somewhat decent on a civic if the car has a bodykit to complement it. The body kit makes the car look larger thus making 18's somewhat acceptable to have.
If not, then having a large wheels like that would just make your car look ridiculous. Especially if you don't even have a drop.
I also used to have 18's on my civic and I tried riding on them for about a month. The ride was the least comfortable of all the wheels I've owned and it tore up my inner fenderwell covers. I'm very happy with my set of 15's and 16's that interchange every now and then. They're a more comfortable ride as the larger sidewalls help absorb road imperfections, plus they're not shredding up my fenderwell covers.