ROB: I disagree with this statement. “Food that tastes bad is inedible for humans.” This is simply false. Taste does not determine if something is edible, or not. You can flavor a piece of leather for example, it is still not edible. On the other hand there are many bland things that are edible.
As for why certain items carry a hechsher, it is because 85% of the market that looks for kosher symbols doesnt due so out of kashrus concerns, rather they look at it as some sort of symbol of quality or purity.