That's because there isn't a distinction anymore between S1 and S2 servers like there used to be. There's plenty of servers available for people with an S1 license to join. Like BreadC and manneF1 said, as long as the server is running S1 content you can join with an S1 license.
Let's face it: If you want to race with road cars and you are not interested of single seaters or GTR you don't need S2. Fern Bay & South City with road cars ftw!
Your friend is right if you're not interested in online racing. Which is what LFS - and any racing sim, for that matter - is all about. Who wants to race against artificial opponents, these days?