Do I need to add an anti-piracy system to my game if I decide to publish it on itch.io or a similar marketplace? The investment to add that system is small, because it's a simple serial code generator.
Don't worry about piracy
Two main reasons:
1) Your game isn't popular enough. (If it is, then it won't be in itch.)
2) You can't do anything about it anyway. (Even major publishers haven't solved this problem with a billion dollars)
But really, it's all about reason 3: people who like your game are going to be generally altruistic. If they did acquire it for free and decide "wow, this is really good" they'll want to support the development. And how do they do that? They send you money. Surprise, now they've paid for your game.
If they don't pay for it, then it isn't something they would have paid for anyway, and in fact, would have been less likely to pay for it with money that wasn't even theirs if they couldn't have gotten it any other way.
Think about it like watching a crappy movie. Sure, you rented it for a dollar from RedBox, but that dollar went more to supporting RedBox because you like their business model. That movie want one that you would have gone to see in a theator, even if you'd snuck in and saw it for free. A good movie you didn't expect to be awesome? Well, now you start paying attention to the director and go see his next film opening night. Or at least, at the theator. Or rent all his other films. And tell your friends about it, and they go rent his films, and so on.
Pirates pirate not because they want things for free, but because they know that 90% of everything is crap and don't want to support it before finding out which things are crap and which aren't. If your thing isn't crap, they'll pay for it afterwards (one way or another, even if it's just telling their friends who all come to itch and pay you $2 for your thing: $2 lost, $10 gained).
I've, more than once, pirated something only to turn around and buy three copies to give away to friends. No joke. Once I found a game called Dragon Warrior Monsters, downloaded a rom to see what it was. Kind of "pokemon in the Dragon Warrior ongoing rpg series" kind of game, played the hell out of it. Sometime later my local video game outlet across the street from my high school had 8 copies come in. I bought one that afternoon, convinced my friend who was standing next to me to buy one, convinced a second friend the next day, and then bought two more to give to two other friends the day after. by the end of the next week all 8 copies were gone and I was responsible for 5 of them. I still know where my copy is, although its save battery has since died.
If your game is offline, and is a simple zipped file, that means if someone downloads it they can send it to other people, which means the average person can "pirate" it.
Do you "need" to put anti-piracy protection? This depends on what you want to achieve. Adding protections most likely means the game needs to "phone home" or needs an internet connection to play even the offline parts, which I personally find very frustrating on games, and I assume others do too.
However people want to sell their games and earn the money they deserve, so there's not many other choices.
Having said that, also keep in mind that piracy can increase the popularity of an otherwise small game. There are hidden gems out there that never managed to become popular even they they deserved it. This means that there are cases (although I don't know how often) where people would earn X amount of money, but because people pirate their content and it becomes more popular, they earn more money, from the people that actually buy it.
To sum it up, do you need to add anti-piracy protection? If you care about profit and do not want anyone playing your game without buying it first, then probably yes.