I'm not trying to argue that it's a bad spell to take, it's just that I personally prefer teleport but have gotten kicked out of uncountable team builder teams on account of my choice in summoner spell. People treat it like a jungler not taking smite. It's really annoying.
Available spells (other than flash): 
ADCs use mostly autoattacks and build essence reaver. Clarity is a waste. QSS > cleanse. You're laning, not jungling. Flash >>>>> ghost.
ADCs are about sustained damage, not burst. Also, they are hard focused so they need a defensive spell.
Exhaust won't save you from long distance abilities, and you can get bursted before being able to apply it to assassins. You need reliability.
You're in a 2v2 lane, heal helps you and your support (and requires little timing), barrier only helps you and needs better timing.
It's not even that heal is mandatory, it's that taking a spell that's going to help you is mandatory. Heal is just preferable because it's just as useful late game as it is early game. Exhaust, barrier, and ignite are less common but still acceptable. Not bringing one at all gives up a lot of lane presence for map mobility that you frankly don't need. You're basically banking on you being able to outplay your lane when you bring teleport.
While i agree with the first poster to reply, i also agree that some people are just meta sheep that can't see the forest for the trees in regards to it not what you take, its how you use it. Pubs just play the meta, but they don't use it, if that can make some sense to you. When a pub is actually trying to do something "off meta" usually you cant have faith in them to know what theyre doing because chances are theyre just doing it to Eff around for the Eff of it.
Things is that low elo pubs usually lack the actual knowledge to turn something relatively off meta into a strength that can work in their favor, especially in blind pick scenarios where you don't know who or what youre going to be up against. In that case its simply better to pick the safer most flexible option.
With that said i have occasionally used 
and 
to relative success.
When a pub questions why you arent using the standard meta summoners on your pick they usually never have an actual reason of their own in mind to question it other than their basic knowledge of what is and isn't typically supposed to be on who
It's not, just highly useful.
In a duo lane, you get the full effect of it when you use it fairly often. It's also easier to use than Barrier since an early use is less punished.
If you took
Exhaust: Fine early game and laning, but as an AD carry you're unlikely to be in position to exhaust key carries since you shouldn't be frontlining. Only the melee carries are likely to be near you to exhaust.
Ignite: Good for early kill/snowballing but if you get collapsed upon by 4 (typical bot lane experience) a defensive summoner will do far more work than Ignite. Also weak for full team fighting.
Barrier: Acceptable if you're laning phase is of little concern, such as a hard farm off lane, when you're against a burstier enemy team. Doesn't happen too often, fairly good for mid lane defensive.
Cleanse: Enemy team is full of back-line hard CC and you need to get out of it. Particularly good against TF, Ashe, Leona, Lissandra, Elise in the mid/late game. Typically you lose early lane or can't do any aggressive plays without dying horribly until you have items.
