I disagree. Although that concept may have had weight in the past, in todays climate there is no real excuse to discriminate because of poor visual acuity.
Standards of corrective lenses are such that an individual can have their vision corrected to better than the minimum requirement, for example the acknowledged minimum is 6/6 whereas in my case my eyesight is corrected to 6/4. And FYI info I have been working in and around airfields for a very long time and never once missed any form of signage, additionally I have been flying recreationally for over 20 years, not PPL(A), and have an unblemished record even though my visual acuity is way, way below JAA standards for PPL
Furthermore, given the inconsistences surrounding this issue globally, your argument lacks weight. The US FAA checks both uncorrected and corrected vision and it is the corrected visual acuity that counts - the applicant is simply issued a waiver if they require corrective lenses. Also, the practice of the airlines to over rule the FAA by implementing their own medical standards I believe was stopped in the mid '90's because it was discriminatory, but I await to be corrected on that.
This is nothing to do with possible legal suits for negligence but more to do with a resistance to change. There is sufficient evidence in place to suggest that this eyesight requirements should be reviewed, indeed it is my understanding that ICAO have been recommending to national regulatory authorities for some time to do this, clearly without much success.
All JAA has to do is simply change the requirement, not hard really.