There are three options with transferring authors rights to ACM:
- Open Access that requires paying >$1k.
- Publishing license means copyright license except that the author continues to hold copyright.
- "Traditional" copyright license.
Everyone author wants to have its paper as more distributed and open as possible without any paywall which directly leads to more citations and so on.
We can remove all money barriers with option #1 (Open Access).
Option #3 transfers absolutely all rights to ACM:
Plus: let's imagine that someone publish your paper with its own name. In that case ACM guaranties that it will defend against this situation, not you.
Minus: ACM can do anything it wants with your work, say, just delete. Or something more interesting as The ACM and Me article says: "Imagine what happens if in the future the ACM goes bankrupt. Creditors could become copyright trolls, sweeping the internet for illegal exchanges of ACM owned papers by academics".
Option #2 transfers not all rights, only an exclusive licence to publish, reproduce and distribute the work. But in this case "... which gives ACM the right but not the obligation to defend the work against improper use by third parties".
NOTE: Each option allows authors to "Post the Accepted Version of the Work on (1) the Author’s home page, (2) the Owner’s institutional repository, or (3) any repository legally mandated by an agency funding the research on which the Work is based."