What I am going to say right now is probably something that will enrage many people. Day 1 DLC is probably one of the most despised practices of modern gaming, along on-line passes. There is many reasons to hate it, and I understand why so many people hate the fact that on the day a game is launched they are already asked to pay for extra stuff, many of them things they were given free before.
The thing is: I don't know how much money videogame companies make. I cannot talk if it is a needed measure to keep profits or if just a scheme to raise such profits. So, I will not defend it as a needed evil. I will defend it as a legitimate business practice and one that the consumer can easily defend itself of.
Let's start with an example. How a car manufacturer convince people to buy a new car instead of an used one? The used car is probably cheaper than a new one. So, what the car manufacturer do to combat the used market? Easy, they don't need to do anything. They just remember people about the disadvantages of an used car.
An used car will deteriorate with time. The paint will not be as good, the engine will have more troubles, the interior will be sullied somehow. The used car will rarely be as good as new ones, and usually when they are they are priced closer, sometimes close enough to not compensate buying used.
Games don't deteriorate over time as cars. A five year old disc, as long as not damaged, will run the same game in the same way as a brand new copy. So, if a new copy is 20 and an used is 10, there is no demerit in buying used.
While movies can make money from theater run, DVD/Blue-ray and digital sales, cable and open TV, games have only one revenue. New copies. So, how the game industry convince people that new copies are better than used ones, if they are theoretically the same? They need to make the new copy more worth having than the old ones.
So, they have two ways to do that: adding stuff to their product that cannot be sold with the old copy or by making an old copy becoming less appealing to the buyer. They cannot do the later, as they can't just delete content of old games or making it don't run as smooth as new ones. So they only have the adding new content to the new copies that can't be sold after.
Enter DLC. Games today are made with DLC planned from the beginning. With this, they can support the game after launch, making people holding on their new copies while waiting for such content. But if the game fail to sell enough copies from day 1, they may not have the money or the prospect of later profit to make this DLC, making doing DLC after launch a risk gamble.
To solve that, they decided to launch DLC on day one and many times bundle it free with new copies of games. Therefore, if you buy new, you will receive more content than used copies and with brand new copies, there is more incentive to the publishers and developers to make more DLC later.
You can say that this is keeping content at ransom. But go to a car seller. Some things in certain cars are optional. The car is made with those optionals in mind and those optionals are probably made at the same time as the car. They are not ripping you off there. They just decided that is the way they will sell the car.
Game makers decide to do the same. They plan the game already with the DLC in mind and reward new buyers with some of them as free. It is their right to decide how they will sell it, since it is theirs until you decide to buy from them.
And it is here where the greatest power of the consumer lies. You don't have to agree with it. It is your right to not accept the form that they sell the product to you and to not buy it as it is. This I have said several times before. You don't have to agree and buy the game new, neither any DLC they launch, day one or not.
I think DLC day 1 is a valid business practice. If you make a product, you have all the right to sell it as you see fit. But I also think the consumer have all the right to not agree with it, by not paying the asked price. If enough people do it, the practice usually stops. As long as consumers make a stand for they believe, of course, by not supporting practices they see as damaging to them.