There are 2 main issues with playing a "tank":

1) Most of the content doesn't require a tank. When you bring a tank to Delera's, what does it do? Sit at the sidelines while the wizard firewall the place?

2) In the content that does need a tank, sensible raid leaders would rather have people they know be the main tank. They will tell you to remove your hate gear, equip a two-handed weapon and be "dps". In the few PUgs where people will let you tank, chances are most of the party is inexperienced. The raids will wipe, and you will be blamed for it.

Save your idea for a tank for when you have an estabilished guild/channel group for raiding and leveling.