> UNSOLICITED IDEA SUBMISSION POLICY
>
> Microsoft or any of its employees do not accept or consider unsolicited ideas, including ideas for new advertising campaigns, new promotions, new products or technologies, processes, materials, marketing plans or new product names. Please do not send any original creative artwork, samples, demos, or other works. The sole purpose of this policy is to avoid potential misunderstandings or disputes when Microsoft’s products or marketing strategies might seem similar to ideas submitted to Microsoft. So, please do not send your unsolicited ideas to Microsoft or anyone at Microsoft. If, despite our request that you not send us your ideas and materials, you still send them, please understand the Microsoft makes no assurances that your ideas and materials will be treated as confidential or proprietary.
I have simple ideas for things such as Xbox Avatar props, costumes, etc. But with this rule, what’s the point of expressing them? It would be a complete waste of time and effort.
Unless it’s something where 343i were to like all of my suggestions so much that they hired me, but that’s very unlikely.
Well from what you quoted the reasons are pretty clear why they do not want to accept unsolicited ideas; being potential legal disputes
However the final sentence also hints that if they do happen to hear such ideas, against their desire, then those ideas will not “be treated as confidential or proprietary”. In legal terms this means they could use said ideas at their full discretion and whoever pitched/came up with those ideas and brought them to microsoft’s attention would have no legal rights whatsoever. (ie: if you really want to tell them your ideas you can, who can really prevent you anyways- lol, but you give up all legal rights by doing so and should not expect any forms of compensation or credit)
On the topic of “why bother having ideas” i dont feel like arguing the point one way or another, although in my eyes it should be pretty obvious why ideas are a positive thing…
I think this statement is in regard to the sending of ideas to Microsoft via any method whether it’s mail, email, or other means.
What’s the point of expressing them? Sharing thoughts and ideas promotes discussion which in turn creates new thoughts and ideas, and so on and so forth.
MS, like any other company, would love to steal (copy) a good idea, make millions from it while you don’t, that’s how companies work. However, what they blam! is the usual crowd of self-proclaimed prophets and geniuses trying to tell them "they have the best idea everz!!11! 
If you’ll but it on a forum, or anywhere, and it’s a good idea MS will hear of it eventually 
If they don’t, then maybe it wasn’t their cup of tea.
I just got the idea for a pet Moa Xbox Live avatar prop, but I doubt that Microsoft would even take it into consideration or whoever is in charge of stuff like that.