Gee, thats why all the "on board" battery chargers come in 3 amp per bank, 5 amp per bank, 10 amp per bank etc. They are all wrong because according to you they should be selling chargers with 25 and 30 amps per bank minimum instead. Take a poll and see just how many people here have a charger that is putting out more then 10-15 amps per bank and you will find them to be in the small minority. (Their charger would look like something from a truck stop and be on wheels) The most popular chargers are going to be in the 5 to 10 amp per bank range. Sure, "Smart Chargers" are generally required but most chargers ARE "smart chargers" today with the necessary built in electronics. 5-10 amps per bank is fine..
Here is Minn Kota's selection criteria. Notice there is no charger bigger then 15 amps per bank and the most common ones are all in the 5-10 amp per bank range. According to you, they'd be selling a product that will harm your battery right? False, because you're wrong in your misguided interpretation of things.
http://www.minnkotamotors.com/products/battery_chargers/select-a-charger.aspx