If we are concerned about ruining the chag or sheva brachos and therefore postpone viewing a potential metzora until later why not say the same for the week prior to this period as well? Is it any different if he is a metzora going into his wedding or going into yom tov?
babak saadatmand, NY, USA
This is an intersting question but it seems that one must say that one has to draw the cut-off line somewhere and in fact one week in advance would not always be sufficient to avoid seclusion later on. Therefore a uniform Din was made and it was decided that only on the actual Yomtov or during the 7 days of Shevah Berachos itself do we say that the Kohen does not examine the Negah.
One can add some reasoning for this. The Rambam writes in Hilchos Yom Tov 7:16 "One does not examine the Negah during Moed lest he should be found impure and his Chag will be transformed into mourning". This implies that if the chag has already started one is careful not to turn it into misery. However if the rejoicing period has not yet started it is not so bad to prevent it starting.
I saw in Shas Lublin that they cite the Rash ben ha'Yasom who compares the wedding to Yomtov. In the same way that Yomtov pushes aside mourning so too the 7 days of wedding celebration push aside mourning, as one sees in the Gemara Kesubos 3b-4a.
CHAG KASHER VE-SAMEACH
D.Bloom
Here is another very straightforward answer to your question. It is simply that a wedding can be postponed and need not necessarily be held on the scheduled day. Therefore as long as the wedding has not actually started and the seven days of celebrating are not yet under way, we say it is preferable to delay them.
It seems that in the time of the Gemara weddings may often not have been such elaborate affairs as they often are today and were easier to postpone. It is true however that the Gemara in Kesuvos 4a states that if all the requisites for the wedding were ready and then the father of the groom or the mother of the bride died, the wedding is not postponed because of the loss of the food and because of the fact that there might not subsequently be someone else available to help the couple prepare the wedding. Nevertheless this factor is not sufficient to justify ignoring the "Nega" of the groom in our Gemara. Even though the Gemara states here that according to Rebbi one postpones examining the Nega in the house in order to save the financial loss of the vessels in the house, nevertheless one can say that losing all the domestic utensils is more serious than losing the food prepared for the wedding.
KOL TUV
D. Bloom