The gun does have to be cleaned "agressively" but that does not mean you have to do the rubber-duck soap and water thing.
You can clean a black powder firearm completely with a solvent such as Hoppe's #9+. I start out with #9+, then switch to regular Hoppes #9. I use patches and a bore brush, and it does not take very long. I do not dismantle the gun, except to remove the nipple on a cap-lock, or the lock on my flinter. When she's clean lube the bore with whatever your choice of lube is. I have never found petroleum products to have any ill effects. Some people like to have kind of a "seasoning" on the bore, much like an iron fry-pan, and I guess pertoleum products will remove that. I'd just rather have my bore nice and clean. Before shooting, I always clean all oil out of the bore.
I know I am in the minority, but I've been shooting BP for about 30 years and have never used soap and water. (I think I did try it once, and then asked myself: "what the heck am I doing all this for??") The only water that gets on my guns is snow or rain. (and sometimes ice) I sure don't want any down my bore and in the breech plug threads, and anywhere else inside the gun. Which ever method you believe in, you do have to completely clean a BP firearm, it's important from both a corrosion standpoint, and getting a buildup of fouling over time, which will "season" the bore in a bad way, fill up the rifling grooves, etc. If rust starts UNDER the fouling, you may not know it until there's some real substantial damage to the bore.