"Our Deans' strongly encourage us to waive our rights because they say programs will not take letters seriously if they know that we (the applicants) were able to see them before they're sent. They think that by having the student see the letter beforehand, the writer will not be honest with their letter. "
My Dean's office said the same thing. I was strongly encouraged to waive my right to see my letters. So I did as they suggested and waived my rights to read my letters. To get around this, you could type a cover letter to the letter writer telling them that you have included two envelopes for them to use to mail a copy of the letter to your Dean's office as well as a copy to you. If you include a stamped self-addressed envelope as well as a stamped envelope addressed to your Dean's office, 9 times out of 10 the letter writer will send you a copy--you made it so easy for them to do.
I did the above with all of my letter writers and got to see all of my LORs. If one of your letter writers doesn't send you a copy, you could just not attach it on ERAS, and no program would get it. Then just ask someone else to write you a letter who will send you a copy. Heck, you could ask 4 or 5 people to write you a letter and choose the best three if you like. Do whatever you want, just be sure to sincerely thank your letter writers for their time regardless of if you use their letter or not. They took the time to try to help you out, so it's the least you can do.
Remember, you waived your "right to see the letter." You did not, however, waive your right to read or even request your letter. It's that simple. You are not breaking the law by reading what a letter writer willingly provides for you to read. You just couldn't legally force them to show you the letter if they didn't want to show you. No matter what, though, you're in control of whether you release a letter on ERAS or not...so release the ones that you read and like. Good luck.