Basically, the lesser of two evils.
At my previous job, I was working on things like Nuclear plants systems or on military systems (not something to "evil" however, it was a part of their ATC system, not something meant to kill people).
And it could be worse, I could work for the finance industry.
Technically, it's quite interesting, it's a large infrastructure, it also permitted me to have my first taste of AWS and Azure and other cool bits of technology.
It was also a big change from my last job where, because of lack of budget, I had to scavenge for old disused servers for the dev infrastructure (yay, Compaq Proliant G1 with dual CPUs Pentium IIIs and 512MB of RAM, I had to use a floppy disk to install Debian on these... in 2012).
It's also not as clear cut as purely sending spam, our system can also be used for password resets, order confirmations or newsletters for example. I am also not completely 100% against marketing (hey, if I create a new product, it is useful to make people know about it), even though I think the world could do with ~90% less marketing. Maybe it's the way I trick myself, that, and simply not thinking too much about it.
It also pays relatively well, not that I'm that attached to having a big pay, living quite frugally, but I'm currently hunting for an apartment, and a big paycheck helps to get the mortgage.
It was also an opportunity for me to work for a big US company and see how it was to work with people all over the world. And it also confronted me with the American Optimism, which is really fascinating, at time annoying because it feels a bit fake, but also at time because it de-inhibits people from not attempting difficult challenges as opposed to a more cautious and critical European mindset. Not sure which mindset I prefer, but still, fascinating.
I'm also not the kind of guy switching jobs every 6 months. I also feel I'm kind of letting other people down if I leave (not completely rational I know). Also, a job is bit like a book, an (almost) never ending book, even if it's not that great, you are still curious about how it will unfold, and it's really hard (at least for me) to leave it in the middle.
At one point, I will probably search for a new job. And finding a job I at least find "neutral" but if possible "benefic" (from my moral point of view) will be high in my priority list.