This will probably vary a great deal between fields and nations, but in classical archaeology at least it is frequently seen as necessary in public communications and relations. These communications have both intrinsic and pragmatic value: the intrinsic value is because, for one, the information we uncover is important and it is important that the greater public learns of it, and two, because archaeological projects usually use public funds and thus the public deserves to have the information presented in a comprehensible manner; the pragmatic concern is simply because, particularly in areas where the rule of law is somewhat lax, the only way to effectively preserve an archaeological site is to engage the public. If a local population finds the greatest value in a site is for looting, it will get looted, if they think its greatest value is preservation, it will be preserved.

At least in Italy, the hard rules are that every reconstruction must be 1) non intrusive, 2) identifiable, and 3) removable. Italy is a leader in restoration methods, perhaps because of its massive archaeological tourism industry, but most everywhere uses some version of these rules. As long as these are followed I have no problem with reconstruction and restoration and find it both necessary and useful.

For the Parthenon in particular, that ship has sailed. It is no longer an archaeological site, it is a work of modern art, and almost certainly one of the greatest.

When you run into a site that has multiple occupation layers over a long span of time, which layer/time period do you restore the site to? The latest one which may be in a state of complete ruin? An older one that may be more complete and perhaps less impressive? How certain can you be on what a building exactly looked like? These are some of the questions archaeologists face and there is no easy answer and mistakes will be made.

Modern academic thought on reconstruction sees it mostly as re-appropriation, or modern monument-building, in my experience. A good example is what happened in Jelling, Denmark the past year; the site had always been a monument to the Danish royal dynasty, and after some excavation a 'reconstruction' focusing on making archaeological information accessible has taken place. The building materials are mostly massive white concrete slabs, and even though this is not a 'reconstruction' in the same sense as the Trelleborg-type houses of Fyrkat and Trelleborg (first reconstruction at Fyrkat, which was proven erroneous, in the '50s and a second attempt at Trelleborg in the '70s/'80s), the purpose here was to convey a sense of place (reconstruct the message of the monument, or in other words, the 'spirit' of the place rather than the actual looks).

Ironically, the budget for the building of the monument was about 10 times that of the archaeological excavations that provided the information, and the builders got permission to dig up stuff that the archaeologists were not allowed to disturb. I'm not bitter. Really.

The reconstruction of the Neolithic burial mound, Newgrange, in Ireland is often criticized for its fanciful - and extremely clean and orderly - presentation of the front portico. It has become an enormously popular tourist destination and numerous mounds of the Boyne Valley remain without the damage, but what was done went way too far. I spent my career restoring historic sites, but there is a reason why the National Park Service offers historic restoration tax credits ONLY IF 75% of the walls survive. One has to start with a building to restore a building, and when the archaeology offers only clues (rather than clear direction), then all one sees in the end is a best guess as to what the site might have appeared.