Because Libertarianism isn't a popular ideology - outside of the Internet, George Mason University and among undergrad Econ majors, and maybe some Young Republicans clubs.
Popularity doesn't decide the legitimacy of an ideology, or what's correct or incorrect. While few people profess to be libertarians, many and many more are becoming distrusting of the government, and supporting less intervention from them in the economy, personal lives, and foreign policy.
How come libertarianism is considered a childish philosophy?
Typical Team Blue vs. Team Red monopoly tactic.
It's harder for the left to demonize libertarians as evil thugs (since they don't fit within the "blood for oil" or "iz muh body you old white man" talking points), so the only way to prevent possible Democrats or liberals from defecting is to just dismiss the ideology off-hand. Like how whenever someone says "hey, maybe we should ask ourselves if this particular law is necessary" the typical bs lefty response is to start shouting "SOMALIA" because apparently you can either want all government (minus abortion regulations) or no government whatsoever. When a libertarian points out how stupid and hackish that logic is, its much easier to just double down on "you don't know anything. You're so immature. Your beliefs are extreme because they aren't our beliefs you child. Libertarianism only works in regards to issues WE care about."
Exactly. I find that strawmen are a favorite tactic of both teams. Liberals think I, as a libertarian, am a greedy, poor-hating c*pitalist, and conservatives seem to think I'm...a liberal. They think in terms of left vs. right, us vs. them, me vs. you, good vs. pure evil. To them, you either agree completely or are...[sinister close-up]...the enemy.
Nothing personal, but libertarians are, generally, how do I say it politely, out there.
Not sure what "out there" means. At a certain period in history, abolitionists were considered "out there." Deviance from the mainstream isn't a bad thing when mainstream leadership has caused all these problems we face today.
Libertarianism has that reputation because of it's simplicity. Stripping the government down to a constitutionalist shell and trusting the corporations of the "free market" to regulate themselves and manage the economy in a benevolent manner is naive.
Not sure why simplicity is a bad thing. Limiting the government in all categories is simple, yes, but it's logically consistent. Conservatives basically say "limit the government, except in social issues" and liberals basically say "limit the government, except in economic issues." In a sense, those are more logically inconsistent than limiting the government in all categories.
Simplicity, I think, is a selling point if anything. It's certainly not a disadvantage, unless your grasping at straws trying to delegitimize the ideology. And I agree that the free market doesn't always work, but I'd rather retain economic freedom, minimal taxes, and try to fix problems in a voluntary manner.
What a clever comeback.
Of course, I shouldn't expect some sort of witty retort requiring more than five seconds of thought from a Libertarian.
My my, sweeping negative generalizations? I would've thought better from a compassionate, kind-hearted liberal!
(Was that too snarky? Eh, libertarians aren't stupid, as you implied, but a bit of snark is a common feature.)