Clearly, whoever makes the first claim on an object of property, necessarily prevents a "first claim" by anyone else who comes after him -- thus leading some to make the assertion that the claimant has "stolen" the item by removing it from possible possession by anyone else. 

Alternately they argue that all property, especially that which is as of yet "unowned", is in fact collectively owned by default by "society".  Such persons invariably argue that property that has been claimed into individual ownership is therefore "stolen", and must somehow be "returned" to society, the state, or to the afore-mentioned "masses".

Such an attitude is neither logical nor reasonable.  Men and women MUST have property in order to live.  So when it comes to unowned property existing in nature, someone has to be first to achieve ownership.

If life can be justified, then property ownership and control can be justified.  Property is necessary to an individual in order to sustain his or her own life.  Ownership is a moral relationship between an individual (owner) and his property.

The person who made the first claim to the land or other item in nature performed a service.  He either bound the land with fence or some other form of boundary, and then either used and improved the land and made it productive in some way, or he refrained from using it, merely keeping it until such time as he made it available for ownership by someone else.  In either case, he served the market.

But is not the speculator merely a thief who claims a property which he acquires for free or nearly free, and then sells at a grotesque profit to others less fortunate in their timing?

Not at all.  The establishment of a claim takes a certain amount of effort, legally and through the establishment of defined boundaries.  Once the claim has been established, it need not be re-established.  It is usually easier and far less costly in terms of human energy to deal with the established owner of a property already bound and owned, than to establish the claim in the first place.