Which is a terrible terrible terrible argument.
It isn't. It depends.
I see it as a long term investment. Let me tell you my circumstances.
I rolled a jedi sage healer at a random realm, started to make friends on start, joined a big guild and GM was AFK. Started a small guild with a number of old guildies. Realm was pretty much dead after december though. My sage got to l47, completed class quest (in many l40 gear, companion starting gear, so it was tough). There was nothing for me to do (as I dislike questing and did not do PvP in WZ; there was not much WZ anyway, and the republic is terrible at PvP on this realm). I took a break of 1-2 months. When I came back, I was still bored with my character. My realm was still dead. I did not know what to do.
I saw a movie about imperial agent storyline and was hooked. I rerolled to a realm where I knew was high pop, and where I knew a friend was playing. I have never played with him since he plays very casual and I did not knew his nicknames until after a few weeks. So then I started, I started making friends on realm, did lots of WZ (the reps are again not very good but we usually get Huttball) and now I am l50 in a guild which cleared all on HM. Casual players, good atmosphere, alive and active.
Eventually I got my sage to l50 too, and joined a casual guild doing raiding, but there is still not much WZ and the realm is pretty much dead. It doesn't surprise me I am often the only healer in WZ (healers never get MVP vote). From my observation in WoW almost dead realms become more dead while active realms stay active. I don't think my sage has a long life to live, sadly...