My what a lot of accusations and hateful things said!
Ok, let's take this from the top. The Pilgrimmage is one of the 5 Pillars of Islam. It's like a Christian sacrament. All Muslims are obligated to go at least once in their lifetime if they are able (healthwise and money-wise). There is a tremendous amount of significance to this pilgrimmage, also known in Arabic as "Hajj;" you are visiting the house originally built by Abraham and Ishmael, peace be upon them both. (although maybe Adam, peace be upon him, originally built it and then it was rebuilt). You are going to the city of Mecca, where the Prophet Muhammad, peace be upon him, lived and prayed, and where Islam was revealed. You along with Muslims from all over the world walk in the same streets that he walked in, and pray in the same way that he did. People who go say it's a beautiful and spiritual experience, and puts you in awe of how large and great the religion is. As a reward for making such an effort to go, God said that he will forgive all your sins up to that point if you make the pilgrimage correctly and with the right intention and sincerity. To answer your question, there are many other ways that sin is forgiven, like fasting the during the month of Ramadan. It's not just for forgiveness of sin, although it's a great perk, but it's also because our Lord asked us to and we want to earn His Pleasure and Mercy.
Now, as to the stampede, what a horrible tragedy. The Saudi government put a limit on how many pilgrims can go a year, something around 2 million during the pilgrimage season, but many sneak in illegally. People are all rushing to get one stage of the pilgrimage done, and there's massive crowds of people. I have 5 friends who all just got back from the pilgrimage about 3 weeks ago and they all heard about it, and probably missed this incident by a half hour. They all told me that the place was unbelievably crowded, and everyone trying to get to the pillars of Mina stage at the same time, causing a rough flow of human traffic that jammed. The Saudi government spends millions on renovating the city, making several-story walkways to help prevent such incidents. Still, things like this happen every year, a stampede, a fire, a building collapse, etc.
Muslims all over the world were upset, and I prayed for my friends as they were there. God promises us that anyone who dies while on the pilgrimage will be considered a martyr and go to heaven directly.