Omer Ups & Downs
Over the past many years, in conversations with some friends and acquaintances about Yom HaAtzma'ut, the following statement - or words to that effect - has been made more than once: If only it wouldn't be in the middle of S'firat HaOmer... I might celebrate it too. 

Then there was the time I wanted to schedule a Yom Yerushalayim celebration for my youth group. I asked the rabbi permission and he said, "sure". (Nice.) I added that we were planning to have live music. Again, "No problem". (Nice.) Then I decided to make sure and avoid a problem at a later time. I said that the celebration would be on 28 Iyar. "Oh", said the rabbi. How about moving it until after Rosh Chodesh Sivan. But that's not Yom Yerushalayim. So do it without music. But that's not a celebration. 

There's an old story about a soldier who came to Chief Rabbi Herzog, and asked if he could get married on Yom HaAtzma'ut. Rabbi Herzog answered, YES. The soldier said, "really?" Rabbi Herzog said NO. But you just said yes?

Correct. That was before you doubted my answer.

S'firat HaOmer is not intrinsically a sad or mournful time. It became that way TEMPORARILY because we temporarily (albeit a long temporary) have no Beit HaMikdash.

Let's go back to our beginning. The first Omer period (a mismoner for then since we had not yet brought the Omer offering in the Mikdash) was an exciting, busy (and nervous) period of time from the Exodus to the splitting of the sea to Mara to Refidim to Sinai, with the Manna and our first introduction to Shabbat and other areas of Mitzvot, with our preparation for Matan Torah. That alone would be commemorated with joy. The next aspect of the Omer was the counting from the barley offering of the second day of Pesach until the Two Loave offering of Shavuot. That made the Omer period very much like Chol HaMoed, with Pesach and Shavuot as the first and last day(s) of Yom Tov. Overall, a joyous period.

Then the Beit HaMikdash was destroyed. And the Barley Offering ceased. And the Two Loaves offerning ceased. 

We can say that at first, there was an emptiness. Without the offerings at either end of the Omer period, the command to count between them became hollow. Then a melancholy crept in. And then the mournful nature of the Omer developed.

The tragic deaths of the students of Rabbi Akiva, specifically during this time of the year, and specifically for the reason stated in the Talmud (their lack of respect for each other) gave the idea to our Sages, so to speak, to introduce a "mild" level of mourning during this period. It still retains its original function – that of TIKUN, repair of character shortcomings and general self-improvement, with the story of the students of Rabbi Akiva as an additional incentive. Events of the Crusades also contributed to the mournful aspect of the Omer.

The ultimate goal of the Omer, however, is its restoration to a festive period celebrating the renewed Mikdash service (speedily in our time).

Lag BaOmer starts us on the Omer upswing. As does the non-mournful days before Rosh Chodesh Iyar or after Lag BaOmer, according to minhag.
Yom HaAtzma'ut and Yom Yerushalayim also are further steps in the right direction. If one feels that the establishment of the State and the reunification of Yerushalayim were each (in their own ways) steps towards the Geula, then they also become Lag BaOmer-like days in the otherwise mournful period that show us the light at the end of the tunnel and challenge us to increase our efforts to become the kind of Jews and people, and the kind of Jewish community and nation, that will truly bring the Complete Geula.