Well, I'm not sure if it would be bad per say, but essentially, you you be taking away the freedom for people to do with that money as they please after they pass. In many cases, people in the US agree that private organizations, such as non-profits, charities, etc. do a slightly better job than the US govrnmt at allocating large amounts of capital.

I would personally prefer a person passionate about cancer research to allocate $1B rather than short sighted, sometimes pork-barreling, legislators.