Say I work at MegaCorp (they make heavy use of Go in some backend systems), and didn't bother making sure I had permission to contribute on MegaCorp time (and thus, contribute MegaCorp IP). I make some PRs to Go which improve the Go garbage collector, which Google happily accepts. These changes help Google and they could help MegaCorp if some of their projects use Go. Hooray!
Somewhere down the line, someone at MegaCorp notices that I've been contributing to Go's garbage collector on MegaCorp time without permission. I may or may not be fired. However, Google has now benefited from what is legally MegaCorp IP without the permission of MegaCorp. If this is in the USA, there's a decent chance that MegaCorp tries to sue Google. That's a headache that I'm sure nobody at Google would want to deal with.
If there was a CLA which I had to sign, saying that I had permission to contribute MegaCorp IP, Google has a document clearly saying that I had permission to contribute MegaCorp IP. This is a far better situation for Google than if they had no such document.
And Google's benefit from your MegaCorp contributions remains the same. MegaCorp legal recourses remain the same.
The situation is exactly the same.
(2) Either way Google competitor has damages on MegaCorp.
afaik, CLAs and "open source licenses" are different things with different purposes. as such, you can have both a CLA and be BSD.
Not the case - they can claim it is so, but a BSD license with extra clauses is not a BSD license.
As an example, many projects demand copyright assignment through a CLA from contributors, which does not add any restrictions to your use of the project allowed through the BSD license. You still can modify, redistribute, ... the source and products build on it as you wish, the CLA is only relevant if you ask the upstream project to merge some of your changes. The BSD license says nothing about how the upstream project has to accept your proposed changes.