Can anybody own an idea? The only reasonable answer is "Certainly no!" Ideas don't come to people from nowhere; they are born as a collective effect, a result of numerous acts of communication with other people. It does not matter how the idea is expressed by a particular person; it can only exist through the wide circulation across the minds and a variety of manifestations in individual activities.
When somebody creates something, one can be sure that the work of many other people has been used, directly or indirectly. Every act is culturally mediated, and thus always borrowing from the pool of forms, skills, trends and tendencies present at the time. It would be as absurd to sue somebody for using somebody else's idea as to sue non-native English speakers for using English!
Why is it so frustrating and annoying when somebody "steals" an idea from somebody? Why is it considered unethical and unacceptable? The origin of such an attitude lies in the nature of capitalism, which transforms everything into trade values, abstracting it from its real content. Thus any product becomes mere representative of a definite amount of money rather than what it actually is. When an author of a book is indignant at somebody's publishing the same under a different name, the presumed original writer (a single person, or a group of authors) does not worry about spreading the ideas expressed and the results obtained; what only matters is who will get the money. Getting profit becomes the principal goal of any work, and sharing ideas degrades to sharing money.
Under capitalism, the principles of public wealth distribution are essentially abstract, being more dependant on the part of wealth already owned than on the owner's contribution into the general economic and cultural progress. For example, of two people with the same idea, the richer will most probably find the ways for its implementation, while the poorer will be bound to lag behind, wasting efforts on mere survival rather than creative development. The former may even be unaware of the others' contribution, never thinking of the privileged position as a gift from the society; wealthy people will hardly ever refer to those who produced their wealth, and they are not apt to nor share the benefits. One person may have quicker access to publishers than another, and use this advantage to publish what the latter only meant. What does that change? They both get their existence from the rest of the humanity, directly or indirectly using the products of the millions of other people, insufficiently compensated, for whom the both "authors" are "thieves", no matter how they "rob" each other.
The notion of authorship has developed with capitalism, and a more reasonable society would never be interested in the origin of anything. If you can do something, do it without any thoughts of the possible benefits. If somebody wants to reproduce the work of the others (probably, without ever knowing them), the resulting growth of the public wealth will only come to the good of the society as a whole, increasing the accessibility of the products. On the other hand, dropping off the priority issues will result in the improvement of the products themselves, since that will remove any formal restriction and the ballast of references.
Living in the thievish society, people have to obey its thievish laws and steal bread from each other; otherwise they won't be able to live on and proceed with their work. There is always a compromise with one's conscience, and different people draw the line differently. The only acceptable excuse is that one's actions help the humanity to get out of the savage state. This, however, does not make things easier for an individual, since it is often difficult to say which actions (or which aspects of an action) meet this objective criterion, and which don't. This is a serious psychological problem.
One could object that, regardless of the economic reasons, simple honesty would not permit people steal somebody else's ideas, and lie. Probably. But the only reason for a lie is that it brings profit. That is, the idea of honesty applies mainly to those who have already achieved a solid social position; in this case any stealth would be regarded as a kind of perversion. In real life, honesty often becomes a weapon against intruders. For instance, a seeker of a scientific degree has to mention the publications of the boss and his team even if they are absolutely irrelevant to the topic; otherwise, there is no way upward.
Stealth and lie can only disappear if there are no social and economical grounds for them. But such a society will never tie the matter of fact to the historical issues. Any reference to somebody else's work will only be possible as an introductory remark, an expression of respect, or a figure of speech.
With truly new ideas, bringing them to the public is matter of courage rather than priority. If a respectable somebody is brave enough to risk his or her reputation and sign to the words of those who have no other way to promote a radical thought, this is a respectable kind of plagiarism that can only be praised. An idea requiring a drastic change in the public mentality has little chance to attract immediate attention; normally, it will gradually penetrate the minds showing up in quite different contexts, in the work of different people in different countries, through either independent development, or as a distant echo of one's direct and indirect contacts. Ideas get passed from one person to another on the unconscious level, through the field of social inclinations and preferences. The emergence of the same ideas in different people is a good sign, indicating both the truth of the idea and a shift in public receptiveness.