That depends on your point of view. It's not like you have to research alien containment, which implies it's "available" at the start. Arguably, most people tend to build it on the first day anyway, and it's not like you shoot down 20 UFOs before it's complete.
It also means you could fully flesh your base at the very start, but you'd obviously start with a lot less money. It would be nice to also have just built two hangers for example, and save money on not having a second interceptor.
Finally, it wouldn't "force" you to buy alien containment... The whole custom base tool was about allowing the player to configure their base to their liking, rather than having to try and build around what the game decided for you.
I'll never change any of it, so it's all moot really