Age verification issues run into some problems with data security and personal ID protections.
Look at how often places like Target, Kroger, or Walmart get their databases hacked and people get mailed 'credit monitoring' offers to deal with stolen ID issues.
Any ID info given to 'verify' a person's age to a porn site, is ID info said porn site can then be targeted for hacking to obtain.
I know the conservative hate for porn isn't going away, but the ways the GOP tries to go after porn are often not up to date with the realities of the digital age and digital age security issues.
Edit: If conservatives wanted to find a sane middle ground on this matter, they first have to understand the issues in play, and not just the ones they want to morally grandstand about. Porn will never go away, but making it safer for the people involved, and making it harder for underage people to access it easily (completely stopping them is impossible), can be done, it just takes both sides being honest.