I also encounter the same thing, this are people who so call think they are very civil mind and that they are doing a favour for the everyone on what they perceive to be a wrongdoing or injustice, more like they have a very different way of looking at thing from normal people. Basically they really nothing better to do and so this way of looking at things helps them feel "bigger"
If people cannot hug in public, who say one? Not even anything illegal? If u want to talk about law, even kissing is ok, correct me if i'm wrong, but personally i also agree on a social level, it's not good for kissing in public places so the line limit should be hold hands and hugging but no sexual simulation.

Once i went out with some friends, then a gal(one of my friend) was wearing tank top and she had a jacket zip up and jeans on, then some old fool about 50 years old i think came down from some mountain never see woman dress in singapore humid weather one, say she was indecent or something... so ridiclious not even funny....and i find very lack of reason for his insults, and it was just a case of a older person trying to boss some kids around. i told him f**king ccb, who are u to tell ppl what to wear? then he still say who are u to intervene and all that rubbish and ask for respect...in the end i scold him fucking cb and told him to fuck off again and turn around cause or else i might whack him so dun see the point as i already did what i wanted to do, tell him off what i think (abeit in a vulgar manner lah) and let him know he should mind his own bussiness in public and not disturb strangers on public transport, not his own house when he can anyhow lecture people.
Even thought obviously everyone who heard our arguement were looking at us, but i heck care since it is none of their business, cause if u don't stand up for yourself, u think anyone will? And i also think alot of older people think they can teach younger people about things but i think respect has to be earned, doesn't mean older person means more capable or smarter. I still stick to my view that respect needs to be earned, don't say u older means u deserve respect. What if a elder is a fucked up who achieve nothing in life and have some really bad character and mindset problem? To respect someone is a very important thing, it means u are saying i want to learn from u , u are a rolemodel and i want to be like you, u think that is true for everyone? Respect and basic courtesty such as saying thanks are different things.