If a BSON object is corrupted, we won't be able to print it out for logging because the process of logging itself may result in a segfault.

For example, if we encounter a BSON oplog entry with invalid fields (say out-of-order timestamps) we will crash when attempting to print the oplog entry if the BSON happens to be corrupt. This means we the server crashes without leaving any info to help debug the issue.

See comments for more info.