I'm not sure how bad your damage is, but, at worst, I'm do half of what a DPS does. Oftentimes, I'm pushing upwards of 2/3rds, and, in the case of pug runs, oftentimes I'm tied or overcoming one or more DPS.
If the only damage that a tank needed to provide was what is necessary to hold aggro, I would barely ever be attacking because I can generate enough enmity in the first 30 seconds to hold aggro off of all of the healers and DPS for the rest of the fight (for longer fights, I would just repeat my 30 sec starting rotation every 2 minutes or so). A tank that only attacks to generate sufficient enmity to keep aggro off of the rest of the group is doing their group a disservice.Damage is not a Tank class's priority beyond what is necessary to hold enemy attention and generally have a large enough HP pool to give the healer something to do.
Since we're talking about gearing here, yes, tanks shouldn't be prioritizing speed, crit, or det above parry or acc, but it's impossible to *only* have parry and acc itemization. You're going to *have* to have some degree of DPS itemization on your gear and, if you're not optimizing said DPS itemization, you're hurting your group. Even if you *don't* think tank DPS is all that high, it's still DPS, and it does actually add up. 10 more DPS on a tank and 10 more DPS on a DPS are the same exact thing.
Ignoring tank DPS just because it's a secondary functionality is just as bad as a DPS refusing to dodge survivable bad shit. It's that kind of mentality that leads to PLDs swapping over to become utterly horrible WARs.