It is allowed because 99.99.. of the transactions WILL be committed so the data you read is correct. It is better that giving you data that is obsolete at the time you read it just because the commit was not done yet.
Adar Yechiel Rechovot, Israel Peter McLarty wrote:
Another common one you see is set transaction level read uncommitted, which on general terms means read uncommitted data. I have absolutely no idea as to why this is even allowed.
