First, lets look at the entire section:
4.4 IMPORTANT DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITY
EXCEPT AS EXPRESSLY SET FORTH IN ISRG’S CERTIFICATE POLICY AND
CERTIFICATE PRACTICE STATEMENT, LET’S ENCRYPT CERTIFICATES AND
SERVICES ARE PROVIDED “AS-IS” AND ISRG DISCLAIMS ANY AND ALL
WARRANTIES OF ANY TYPE, WHETHER EXPRESS OR IMPLIED, INCLUDING AND
WITHOUT LIMITATION ANY IMPLIED WARRANTY OF TITLE, NON-INFRINGEMENT,
MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE, IN CONNECTION
WITH ANY ISRG SERVICE OR LET’S ENCRYPT CERTIFICATE.
BECAUSE LET’S ENCRYPT CERTIFICATES ARE ISSUED FREE-OF-CHARGE AS A PUBLIC
SERVICE, ISRG CANNOT ACCEPT ANY LIABILITY FOR ANY LOSS, HARM, CLAIM, OR
ATTORNEY’S FEES IN CONNECTION WITH SUCH CERTIFICATES. ACCORDINGLY, YOU
AGREE THAT ISRG WILL NOT BE LIABLE FOR ANY DAMAGES, ATTORNEY’S FEES, OR
RECOVERY, REGARDLESS OF WHETHER SUCH DAMAGES ARE DIRECT,
CONSEQUENTIAL, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, PUNITIVE, OR
COMPENSATORY, EVEN IF ISRG HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
DAMAGES. THIS LIMITATION ON LIABILITY APPLIES IRRESPECTIVE OF THE THEORY
OF LIABILITY, I.E., WHETHER THE THEORY OF LIABILITY IS BASED UPON CONTRACT,
WARRANTY, INDEMNIFICATION, CONTRIBUTION, TORT, EQUITY, STATUTE OR
REGULATION, COMMON LAW, OR ANY OTHER SOURCE OF LAW, STANDARD OF CARE,
CATEGORY OF CLAIM, NOTION OF FAULT OR RESPONSIBILITY, OR THEORY OF
RECOVERY. THE PARTIES AGREE THAT THIS DISCLAIMER IS INTENDED TO BE
CONSTRUED TO THE FULLEST EXTENT ALLOWED BY APPLICABLE LAW.
BY WAY OF FURTHER EXPLANATION REGARDING THE SCOPE OF THE DISCLAIMER,
AND WITHOUT WAIVING OR LIMITING THE FOREGOING IN ANY WAY, ISRG DOES NOT
MAKE, AND ISRG EXPRESSLY DISCLAIMS, ANY WARRANTY REGARDING ITS RIGHT TO
USE ANY TECHNOLOGY, INVENTION, TECHNICAL DESIGN, PROCESS, OR BUSINESS
METHOD USED IN EITHER ISSUING LET’S ENCRYPT CERTIFICATES OR PROVIDING
ANY OF ISRG’S SERVICES. YOU AFFIRMATIVELY AND EXPRESSLY WAIVE THE RIGHT
TO HOLD ISRG RESPONSIBLE IN ANY WAY, OR SEEK INDEMNIFICATION AGAINST
ISRG, FOR ANY INFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS, INCLUDING
PATENT, TRADEMARK, TRADE SECRET, OR COPYRIGHT.
The first part that you notice is that in the first section is this sentence:
LET’S ENCRYPT CERTIFICATES AND
SERVICES ARE PROVIDED “AS-IS” AND ISRG DISCLAIMS ANY AND ALL
WARRANTIES OF ANY TYPE, WHETHER EXPRESS OR IMPLIED, INCLUDING AND
WITHOUT LIMITATION ANY IMPLIED WARRANTY OF TITLE, NON-INFRINGEMENT,
MERCHANTABILITY, OR FITNESS FOR A PARTICULAR PURPOSE,
Which basically says that "we won't provide any statement to guarantee that our services/certificates don't infringe on another work, or that they are fit for your particular use".
The real point of this indemnification section is in the second paragraph:
BECAUSE LET’S ENCRYPT CERTIFICATES ARE ISSUED FREE-OF-CHARGE AS A PUBLIC SERVICE, ISRG CANNOT ACCEPT ANY [...]
They are too poor to afford lawyers, so they are saying that you must agree not to sue them if you suffer any damages as a result of using the service/certificates. This is not a license granted by you to steal anything you don't expressly give them license to do so.
Let's take an example:
Let's Encrypt (LE) gives you (Customer) a certificate. That certificate, knowingly or unknowingly, infringes upon a patent owned by XYZ. XYZ sues LE and the judge orders LE to revoke all certificates using XYZ technology. Your site is now shown as unsafe and your payment process doesn't work. You lose $100k in revenue getting your site back up with another certificate company. According to this agreement, you cannot sue LE for that.
XYZ could go even further and sue you, even though you unknowingly had been using that patent. Again you can't turn around and sue LE to recover anything XYZ recovers from you (or even the fees you spend to win).
What you are not granting to LE is a right to "steal" any technology on any site/system that the certificate or service is used on. This agreement, in its entirety, is between LE and you for the use of LE services/certificates. Even if LE somehow steals from you, this would not indemnify them for that.
