You can have fun with a wide variety of people. It may require letting go of your preconceived notions of "fun" and being open to new experiences, though.
"Have fun" != "fix". If those concepts are crossed in your mind, that could be part of the problem. Just don't date the people who need fixing - or if you do, make it clear that they are responsible for fixing themselves and you're not going to do it for them.
There are lots of people in this world who don't need fixing and can be quite fun to hang with.
I think those who are 'fun' to 'fix' are therefore at risk of dependency on that. Like a drug.