I present a scenario here to Libra/Jag.
Suppose member "T" is selling a stolen/accidented car here (without anyone's knowledge) , his car has been up on the forum for almost 2 months. T has had a member come over to see his car 40 days ago, but didn't like it due to some problems.
After 2 months T try to reactivate his thread, of selling his car. A new/unaware member contacts T to see the car.
1) Had T been given the rights, T would have wiped out the replies revealing the truth about his car and thus somebody would end up buying a stolen/accidented car from T, courtesy of PW.
2) If member T like other members did not have any rights of modification to his thread, some caring and informed member would have revealed the truth about the car, which would secure any potential buyer's money and PW out of any potential legal hassle.
Therefore, please, DONOT think about giving modification rights to posters, as our young members donot exactly know the perils of this world.
Disclaimer: T is just a presumable member, this presumption just not point finger to anyone.
Allah hafiz.