It is a bad thing, and something most other protocols do NOT do. A
bad TELNET escape sequence is an error, it doesn't shutdown the TELNET
session. A bad MIME encoding is an error, it doesn't shutdown a SMTP
session. A bad route is an error, it SHOULD NOT shutdown a BGP session.
Cisco should fix their implementation AND the RFC should be revised not
to require tearing down the BGP session because of one bad route.