I think it would be hard to argue that the ADA is a bad law, however. If it's not a bad law, it should not be optional. Otherwise it's not, by definition, a law.
We live in a society with many optional laws already.
This law was put in place to protect hearing disabled people not punish everyone else. It also wasn't intended to deprive the world of 20,000 free lectures.
Perhaps these videos could be granted some kind of temporary waiver until they can be closed captioned. Youtube even has system for community driven captions. People have suggested crowdfunding projects. People have lots of ideas for fixing this.
If the videos are down the incentive to make them available to the deaf is removed. Some kind of optional application of the here could incentivize a fix that works for everyone.
In many ways.
People ignore speed limits pretty frequently. Traffic flows faster, more efficiently because everyone is breaking the law.
Laws against gay marriage and other discriminatory laws. Society is greatly improved by making them optional. Some states have strange and bizarre laws in the books but nobody is bothering enforcing them. Everyone treats them as optional and the society is better for it.