Am I unwittingly damaging my knives with amateur sharpening?
Destroy is too strong a word. For most knives the worst you can do by honing wrong is to take the edge off the knife. This isn't destroying it, it just means you need to get it sharpened again. Angle is the important thing with honing, you need to match the sharpened angle and be consistent. 

If you have a knife with a design or a pattern on the blade, like Damascus steel, some Japanese knives, etc. honing badly could damage that design or pattern and ruin the look of the knife. That doesn't destroy it, just makes it less attractive.