Hi ShayanMirza!
I have seen this question debated here before, and doubtless is has been debated in the old forum as well. I think that objects of all kinds have been stolen and looted from many peoples throughout man's history and used or sold elsewhere. The cultures from which these items come may even have sold them to acquire money, and indeed many were originally produced just to satisfy collectors demand. What is now revered as an antique weapon may have been made as an old "tourist knife". Now consider that presently, many cultures around the world do not have the interest in old weapons and traditions anymore, and if they do, they often lack the funds to sustain collections in musea. If a family is poor, it may certainly choose to sell an heirloom to survive. That item passes through many hands before reaching a final collector and staying there for a while.
If Europeans had not conquered, someone else always did, so the really valuable and precious items were always looted and given off as pretty things or as presents. European nations built large empires, so I think it is natural that they have large stocks of ethnographic artefacts, especially since they did have interest in mysterious "oriental" cultures.
In many places, weapons have always been recycled, either for their steel or for their precious decorations. This would continue if not for collectors who wanted to keep the weapon as it is.
I think that from the numerous discussions on this forum you can see that most members love to learn about the cultures that produced the weapons. These are certainly not just pretty things to put on walls.
As for ebay, consider that many people use it because they need the money. Whether they had an uncle who collected or stole the weapons and artefacts, they are now selling them because they are in need, not necessarily out of greed and desire for profit. Years ago, weapons that are nwo very expensive were sold for peanuts, and some still are.
I think that if not for collectors, a great deal of weapons, artefacts and knowledge would be lost
And I think most members here would sell a couple of their relatives to travel to the places that produced the weapons and learn about them
In some past discussions, some members even considered offering their collections back to the countries that produced them. But then, how would they be cared for? Musea care for valuable, unique pieces, not the regular simple examples that make up many of our collections.
Emanuel