proper use of defensive abilities, and more importantly how to get past and kill a defensive minded opponent is an important lesson when playing a fighting game.
It's not cheap to use them, and your friends will only get better if you do your best.
That being said, if you're stomping your friends all the time because you're clearly better then they are, use the handicaps. Trying and give yourself about a 50/50 win/loss ratio against them, perhaps by heavily handicapping yourself, until they get better. Once they get used to fighting you, you can turn the handicap off.
I was similar in SC4. I made very effective use of the block ability, much to the frustration of my friend. However, he worked on beating my blocks, and eventually he got better then me... then I worked on getting better at him, using different techniques.