I don't think it ever has been. Look at CSS.

court ruled that the DMCA statute does not require the access control or copy control technology to be strong as long as it prevents unauthorized access and/or copying under ordinary course of operation and with the authority of the copyright owner

I don't think so. Pretty sure it's "effective" as in "has the effect of" not in the sense of "does its job well"

Exactly, it's like a Home Depot lock, sure you can smash it, you can easily pick it, but it's effectively a lock.

That's subjective.

Any strong technique, once broken, is not effective anymore: is it then legal to use such technique, due its ineffectiveness?

Also IANAL but from what I know the law has not been interpreted to use (in my opinion) a reasonable definition of the word effective. The law requires 2 things here for a covered protection to be "effective":

  #1 That the protection on the copy is "sufficient" to protect the rights of a copyright holder of the original work, and

  #2 That the copyright owner is satisfied with the protection provided by the copied work.

To me at least, this seems insane. You can theoretically claim DCMA based relief for anything forever by taking its bitstream format and flipping every bit once. That coupled with the knowledge of the copyright owner will be enough to be covered under this reading of "effective".

The linked court decision states on page 28:

98. To prevail on a DMCA claim for violation of the copy-control provision, plaintiff must show that CSS “effectively protects a right of a copyright owner under” the DMCA. 17 U.S.C. § 1201(b)(1). Under that section, a technological measure “effectively protects a right of a copyright owner . . . if the measure, in the ordinary course of its operation, prevents, restricts, or otherwise limits the exercise of a right of a copyright owner under this title.” 17 U.S.C. § 1201(b)(2)(B). For the reasons articulated above, the court finds that CSS technology is an effective technological measure to prevent copying of copyrighted DVD content by the average consumer. That CSS technology has been hacked does not disturb this conclusion.

The RealNetworks case where this was decided is linked below. The case basically went "There is this program that uses freely available code that technically breaks your DCMA approved protection method, CSS, but because CSS still works to protect rights due to the breadth of it's implementation, it is not sufficiently broken by your program or the freely available knowledge you used to make it, and the Court finds for the Plaintiff." (my interpretation from reading page 56)

See: https://www.eff.org/files/filenode/RealDVD/real_v_dvd-cca_pi...

Pages #28 and #56

There was an argument for this, but it was in the EU not the US. http://www.turre.com/finnish-court-rules-css-protection-used... No idea how that ended up going in courts or later legislation.