But it can be...
You see, it I decide to take my neighbours land then that is... Stealing!
The current conflict is an internal, civil conflict between two competing ethnic groups for possession of territory within a set of established international boundaries (short version: Syria to the north, Jordan to the east and Egypt to the south). There has never been a permanent, international, boundary within this territory dividing land that is under the sovereignty of Israel and land which is under the sovereignty of Palestine. ALL legal documents regarding the two-State solution (a solution you and I generally agree upon) demand that the final border between these two nations be negotiated between them. Therefore, neither side holds legal sovereignty (ownership) of the territory and neither can be stealing from the other. It is not possible to steal something whose ownership is in dispute.
Now, I THINK when you say that Israel is "stealing land" or "taking my neighbors land" you are using the Green Line as your basis for determining sovereignty (ownership) by each party. Therefore, you are claiming that any territory on the eastern side of the Green Line belongs to "Arab Palestine". This is a false premise. The Green Line is the 1949 Armistice Line between Israel and Jordan. Not Israel and Arab Palestine. Jordan. Why is there an Armistice Line between Israel and Jordan? Because Jordan crossed her international boundaries, using military force, and attempted to establish sovereignty over territory which was not hers. Remember that whole thing about it not being legal to steal land from other sovereigns through use of force or war? Oops.
Jordan, eventually, removed her military and government forces, abandoned that territory, renounced all claims to it and made a peace treaty with Israel. What does that do to an Armistice Line? It makes it disappear. There is no Green Line. It no longer exists for any purpose because the purpose was simply to pause the conflict between Israel and Jordan.
To claim that that land is now "Arab Palestine" is simply not correct. While the expectation is that the Green Line will serve as a basis for negotiations -- the Green Line itself represents nothing legal with respect to the internal, civil conflict between Israel and the Arab Palestinians who are seeking their own sovereignty. The solution to this internal conflict, as has been the solution to all such internal conflicts, is the division of territory and the establishment of borders through negotiation and treaty.
Therefore, to say that Israel is "stealing someone else's land" is legally false. It is not helpful because it paints the one side as "bad" and puts the onus on the one party to "correct its behaviour". It would be much more fair to claim that the territory is disputed. The only way to solve a dispute is to negotiate a solution between the parties. This makes BOTH parties responsible for the outcome, rather than only the demonized one.