It's not about being "two-faced" or anything of the sort, it's about what you feel is value for money and what isn't; what provides a meaningful addition that you're prepared to pay for, and what you feel should have been included in the first place because of how utterly trivial and unimportant it is. If it's so trivial and unimportant why do people complain? Simple human nature, and some of us can remember when these things WERE included, so naturally we're going to complain about it.
That said, DLC is not an entirely negative thing, as it allows developers to keep supporting their titles with additional content after the game's initial release, and some companies - not many, but some - do use DLC this way. Hyrule Warriors on the Wii U is a good example of DLC done right, where you had free, trivial content and more meaningful game modes in the form of patches on top of the paid downloadable content packs which gave you additional characters. Typically, DLC with large campaign expansions is generally regarded as worth the purchase too, as it takes some time to develop it, is clearly not cut content, and extends the life of the game by a reasonable amount for what you are being asked to pay.
Microtransactions are a question of presentation and honesty. If a game has microtransactions to begin with, then you know what you're getting into; you're prepared to accept that you're going to have to pay more on top of the asking price unless you're willing to put up with not having a few things. A game without microtransactions is implied to be a complete experience - even without considering the DLC that might cut out small things - and suddenly adding them in is completely outrageous; it's introducing a pay-to-play economy into a title that was originally advertised without it.
All DLC, no matter what it is, is a single one-time purchase: once you've bought it, it's yours to keep. Microtransactions are a continual, steady drain on resources that you have to keep buying for the optimum experience, or what is implied to be the optimum experience. The only thing the two have in common apart from being additional purchases outside of the base game is that they create a has-and-has-not psychology; where you're going to feel pressured to buy these things otherwise you're going to feel like you're not going to get the full experience, or one equivalent to what other people are getting and, in a multiplayer-focused game in particular, that's a huge factor. The biggest difference is that pay-to-play factor that comes with microtransactions, which is NOT something you expect in a so-called AAA title you already blew £50/$60+ on. When they're not there to begin with, it's tantamount to false advertising. It's poor customer treatment at the very least.
The bottom line is that some people are going to feel that some DLC is worth their money and that some isn't. A lot of people see it as mandatory because of what it is and how it is presented, although personally I've always seen DLC as optional addition: if it's going to enhance my experience, no matter what it is, I'm going to buy it. If it doesn't, I'm going to ignore it...well, more likely I'm going to complain about it, but that's human nature. It's not particularly two-faced to have standards. What IS two-faced is the practices of the AAA industry and the whole psychology behind DLC and microtransactions. Sometimes developers just push a little too far, but then we do encourage them by buying the things in the first place.
