Just like Sleeping Poppy said, it depends on how the contract was forged and whether it is mutually beneficial or a parasitic relationship. It also depends on whether control is being exerted on someone else, if their will is bound, and if their life depends on the person who summoned them. All in all, if you're given dominion over another being and they are at your mercy, that's where the morality issue comes into play. It does scream 'slavery' to me though but when fiction explores it and the implications between the two characters and their dependency (co-dependent or on one or the other), it sheds more light on the issue.
Like for instance, in Howl's Moving Castle, Calcifer was caught by Howl and the two of them formed a contract where their lives were bound together. Calcifer wasn't at Howl's will, he had his own personality and his own wants and desires, and they grew to accomodate one another. His greatest fear was dying and killing Howl and Howl's was the same in vice versa, over time they grew more worried about one another and called each other their friend because of their bond. And even when Calcifer was freed, he returned to be with Howl and Sophie.
Depending on the individuals enraptured in this twisted thread, the contract changes.
For that matter, I don't think people should have summoning especially in the real world. If so then Bloody Mary would be haunting every teenage party in the 80s.