It seems to me a more effective solution than an open letter for tech giants would be one, or all, of the following:
+ Refuse to give any money to any political candidate.
+ Refuse to sell your products to any governmental agency. Including SaaS products. (Never going to happen, but would be great.)
+ Create a pooled ad budget (like the one to promote this letter) to run ads (video and print) demanding reform.
This will never happen, but I still occasionally dream.