I must say i'm on the fence here... Sex isn't that important, and the 'Don't worry about it if you want to have it' advice is likely correct.
But i do think that taking your time to think through your moral position is a good thing. I guess i'd say you should worry about it when it happens. Sex, whether casual or regular is nice and you should worry about the emotional impact - but it is like diplomacy, two boards which look the same could be very different depending on how the players feel about each other.
You really need to know how you feel and be able to empathise with people to get a good idea if a particular sexual encounter is morally acceptable...
That said, there is massive pressure in society to have sex and be good at it (as people mentioned above) similarily massive pressure to get married (cause who would want to find fullfillment while alone??) it is just assumed...
Sex is not that big a deal, it's like a rollercoaster. I mean sure rollercoasters are fun, everyone likes them (well some people are a bit scared of the idea) but they're not a big deal... If that approach is taken with sex (with all the relevant safety concerns, cause you really don't want to go on a rickitty old one that lools a bit rotten) you should be fine.
Also there are many kinds of sex and no 'right' way to do it, some people like different things and it's not all about the penis and cumming. Orgasms are great but there is lots of fun apart from that, and the emotional impact of trusting someone and bonding with them can be way better. (like wine and cheese, sex and love are each great on their own, but they much better together - and i say this without advocating any religious or moral position, while being completely anti-marriage; i'm basing this on personal opinion and not the lies engrained in our culture, either fairy tale happy endings, the sexual idol worship of our media, nor any bias apart from my own morality, rational thoughts and emotional understandings.)
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As putin mentions we have a problem. Population and economic growth go hand in hand, they are aspects of a culture dedicated to self-preservation and self-promotion. The self-preservation is evident in putins post, he wants to save something; but it is everywhere, the thing that don't self-preserve died out a long time ago.
However growth may not be possible, and halting population growth may trigger a downward economic spin... We do need to be aware of what's going on and i think replacement rate reproduction males a lot of sense, but we ma be over the carrying capacity. I should be ok if we mere stop feeding our meat animals tonnes of protien which we could provide for hungry humans... Or don't have kids til our parents die...w