I have seen it again on a TV re-run, this time on a proper TV and recorded it, and for the first time saw very clearly the gun in Meredith (odd name for a guy!!!) Hunter's hand.
It was clear he went straight for the stage with the intention of shooting a member of the band, obviously Jagger. He got as far as aiming the gun when Alan Passaro stabbed him. It seems likely to me he was after some kind of infamy, like Mark Chapman almost exactly 11 years later, and would have done this regardless of whether the Angels were there.
My contention is that if the police or a private security firm was on duty (or especially Wavy Gravy's "Please Force" as used at Woodstock), they would not have the ability to react so quickly and decisively as the Angels did. The police would not have been able to shoot due to the large crowd. Many Angels of the time had experience of close quarter combat with knives, as many were Korea or Vietnam veterans.
I therefore consider that, as it turned out, it is very fortunate indeed for Jagger's sake, and for the sake of everyone else on the stage at the time, that the Angels were present. I think Jagger has the Angels to thank for the fact that he is still alive today.
On a side note - does anyone know anyone who has lipreading skills? I would love to know what the audience members at the side of the stage are saying to Jagger just before the stabbing.