I'm sure you've heard of malpractice right? Where you have people who don't know what they're doing, acting like doctors?
Same is true in D&D, now. You don't want someone trying to cure you of diseases if they don't have a good Heal skill.
Keep in mind; to have learned the ritual in your book, you've gotta be level 6. Presumably, you've got a positive Wisdom mod, and are trained in Heal, too... 1/2 level + 5(trained) + 3 (Wis) is... 11. The 'level of the disease' acts as a penalty, so say it's level 6, you're now at a +5. Odds aren't bad, 20% you take 100% damage, 50% take half damage, 30% take 1/4 damage. You can then sit and heal up by burning surges(with maybe a death stabilization heal check made by the healer in case of a bad roll). Given how bad disease tends to be, I'm guessing it'd be worth it, in a lot of cases. You might wait until after an extended rest (if you can) so you've got Surges to spend on recovering from being cured; but I'm sure it'll be used.