Normally I don’t respond to these things, but I just want to say this:
Nobody hates Mako because of his “rough childhood.”
They hate Mako because he’s the television equivalent of a thinly-veiled Mary Sue character in a bad fanfic (often called a Gary Stu or Marty Stu.) They hate Mako because everything else in the show has been almost perfect until the main plot itself got pushed to the backburner to make sure nothing bad or negative ever happened to poor baby Mako. They hate Mako because, lo and behold, if you actually cut out all the scenes where Bryke tries to shove a rushed love story down the audience’s throat and just leave it as a story about Korra fighting to become the Avatar and to save Republic City, well… you’ll have a pretty complete, decently-wrapped up story. 90% of Mako’s scenes are disposable and unnecessary.
There are fans who hate Mako because of his personality and overall generic nature, yes, but almost everyone that doesn’t care for Mako (notice I say “doesn’t care for” instead of hate,) can largely attest to it being a result of bad writing.
Meanwhile, Tarrlok was evil, yes, and as an antagonist he is “hated” appropriately, but not hated in the same way as Mako. Tarrlok had a complete story. Tarrlok rose to power and fell because of his own avarice and blind conviction. Tarrlok made his mistakes and got the ending that made our hearts break. But what about Mako? Mako made mistakes and got the cake for it, so to say. Mako was protected at every turn by Bryke and it’s just very pitiable to play a game with a character who is largely “indestructible” like Mako. It’s like when you’re ten and playing cards with your friend but they do everything irrational and insist they can never lose because they’re just *that special* — this is why Mako is hated. Mako is just *that special* to Bryke and it’s going to take a lot to convince otherwise.