To those who say zerg can react super fast upon seeing an air unit: You are most likely the main trolls, if you see a banshee or void ray, it's already too late. Even assuming you took the lair tech(which is already guessing that the opponent went for air tech, since lair tech is guranteed loss vs infantry+tank push or 4 gate push), your queen and most of your drones would be dead by the time hydralisk den finishes if you started building it AFTER seeing the air. I know this, so I just build 2 evolutionary chambers the moment I get a glimpse of an air unit and it has never saved my ass in any of my game since 1) by the time evolutionary chamber finishes, my queen is dead and 2) if my evolutionary chamber does finish, because the opponent focused on killing drones first(this is obviously worse for me), I now start building about 10 spore crawlers, none of which get even half way done.
To those who say I'm bad for not willing to sacrifice an overlord to get priceless intel: First of all, 100 minerals is nothing to laugh at, especially that early in a game. I also already mentioned in several posts in this thread alone that I do in fact sacrifice an overlord and also mention that it's dead at least half the time before getting to see anything meaningful to 3 marines or two stalkers. What the hell did I get out from tossing 100 minerals away? I got to see some pylons and 2 stalkers? The damn thing flies so slow that you should be perceived as a bad for letting an overlord scout anything meaningful.
To those who say it's a narrow window of time that the terran/protoss player has and it is their given right to exploit this opportunity: This narrow window of time between the time you can get a drone in and before overseer or speed upgraded overlord comes out is arguably the most crucial point of the game: It is when people take their tech or mass tier 1 army to do a heavy push with. Frankly, scouting isn't even necessary extreme-late game when army composition is grossly obvious; It is this early to mid game transition where the opponent is either stupid-vulnerable(techd to air or other tier 3) or an extreme threat(massed tier 1 nonstop). You can lose if you don't know what's coming at you, as I mentioned in almost every post I've written in this thread; I'll even mention it again: Against a walled protoss for example. You see 1 gateway and 2 pylons blocking entrance, there are 2 zealots, a stalker, and a sentry visible. What do I do? Most of the time I predict a heavy gateway unit push, since I've bitten the dust too many times to this crap, but way too often I build spine crawlers and some zerglings to defend to be greeted by 2 void rays charging up on my hatchery. I'll say this again: if you do not get spine crawlers aginst a 4 gate, you aren't stopping it without putting even more resources into units. The obvious problem here is that you literally have no way of knowing if it's air tech or 4 gate with the 2 MPH flying wonders that cost valuable larvae and 100 minerals.
To the guy that says scouting with barracks is unique and would be hilarious: You must be either trolling or not realize how utterly overpowered this is. It costs half the scan's cost, is permanently there until killed, and is literally a 1000 HP overlord that flies faster. People did this in professional korean starcraft leagues in SC:BW and people do this now if they want to scout without being retarded(hurrr I want to spend 300 minerals to look at my opponent's base for 10 seconds rather than spending 150 minerals to fly straight across his entire base, then get to fly over it again 2 minutes later to see if anything's changed). I'd love nothing more than a new zerg structure named the flying zergling: 2 minute build time(yes, I'd settle for that), 100 minerals, 1000 hp, same flight speed as barracks. Funny thing is, people will scream overpowered at this.
Last but not least, the guy who suggested a starter drone hiding in the opponent's base to SURPRISE SCOUT HIM AT THE MOST CRUCIAL TIME! I will admit that I didn't even think of that, and I will also admit that it'd work at least 90% of the time since people wouldn't scout their edges for hidden zerg units after walling off, but... 1 drone out of the initial 6 you start with? The opportunity cost there is pretty much immeasurable for that drone. If this was troll, well played.