I don't know that any parent of a child who may have suffered a vaccine injury is looking for something to blame. I think they're trying to find how to fix the damage, as soon as possible, and with as much information as possible. But, as we all know, there are an awful lot of roadblocks--some of which are intentional--put in the way of treating, even identifying vaccine injuries.
I think it is pretty natural, when something goes wrong with our children, to look around and see what might be the or a cause. I don't think blame is a bad thing as defined by the dictionary ( Blame is defined as: to hold responsible; find fault with; censure. ) but it is a loaded word. I will reword - I don't think parents are picking something out of thin air to pin autism on. I think some might blame vaccines on some level, but I do not think they are looking for something to blame
I also think it is natural (and fairly brave and noble) for parents who have vaccine injured children to let the world know what happened and that they believe vaccines injured their child. They are trying to add to a body of knowledge and let parents know that these things happen.