It's the same stigma of walking nude and having sex in the public, like in Orchard Road or Holland V, etc.
But the grey area starts when you walk around naked in your flat with the windows and blinds pulled aside.
You're in your own flat, so it's private, but you can be seen from across your flat, so it's public.
Same as the public blog. No one put a gun to someone's head to read the blog.
There're 500,000,000 websites and 1 billion facebook accounts and increasing. No one forces anyone to read.
So, I think it's just being bitchy by those who cry foul and use the "immoral" tag on the couple.