It's definitely better to keep the screenshots viewable without registration. Just make the registration tempting in a more honest fashion, such as the community that awaits, and how the community may benefit that new member.
No need to sweat it though. There will always be a few people whining, who pretend like they speak for everyone, whereas they're only speaking for themselves. What they don't realise is that they're wrecking the very premise of 'democracy' itself dictating how things should be.