It's not "nice" but that's to be expected.

When you're out experiencing "life" you'll run across people who take and other people who give. That transcends all sports. Cycling is no different. When I encounter a situation like yours where I catch a slower rider and they want to cling to my wheel to keep up, I'll do it for a few hundred yards and if they don't do a pull, I get up from my saddle and drop them if I can.

Now mind you, this does NOT happen often with me because there are lots of faster riders in my area, but it does happen occasionally. Try doing the same and don't get worked up over wheel suckers. On the other hand, I have been known to slow way down to force the rider to make a decision to go around or be an obvious wheel sucker. I rarely do that and only if I'm in a bad mood that day, which is also very rare.