This depends a lot on intent and tone. While it's hard to get both online, you can usually get the jist through context.
"Boxers have great punches, but they don't have kicks. If you want a well-rounded striking game, you should add something with kicks, like kickboxing or Muay Thai."
"Boxer's cant do anything but punch, Muay Thai has everything."
Notice the difference between these two? The first one acknowledges the punching skill you will learn in boxing, but offers ways to improve
if you want to know how to do more. The second just assumes that Muay Thai is objectively better than boxing because it has more than just punches.
All of it is competitiveness between martial arts. Competition can be a good or a bad thing.
There's a guy in my BJJ gym who was around my size when we started (but he's lost a lot of weight since then). He and I started around the same time, are both regularly in attendance, and both do a lot of research outside of class. We're roughly an even match for each other. We enjoy drilling together, we enjoy chatting before and after class. When we roll, it's usually 50/50. He's the guy in class that I test myself against. Not the new 100-pound teenager. Not the guy built like a basketball player. But the guy that I'm usually 50/50 with. I test myself against him, he tests himself against me, and whenever either of us does anything cool, the other says, "That was awesome, show me how you did that!"
This is a good rivalry, good competition, because we push ourselves to be better, and we have a stronger relationship for it. But instead, let's assume that I did one or both of:
- Whenever he beats me, I get frustrated. I call him names to take out my anger on him. I either do the most painful technique I know out of revenge, or I just get so lost in the emotion that I get beat even easier, and it's a downward spiral.
- Whenever I beat him, I gloat. I call him names. I brag to everyone that I tapped him out. I make sure everyone knows how great I am and how bad he is because I beat him!
In that case, I'm either a sore loser or a sore winner (or both). It wouldn't help my training. It wouldn't help his training. He wouldn't want to train with me.
If I were to say to you that "Kung Fu is stupid", or talk in such a way that you inferred as such, I'm sure you wouldn't want to talk to me about Kung Fu. You might want to argue with me. But not talk. And that argument wouldn't be productive.
However, if we were to discuss the differences between Kung Fu and Taekwondo and what we can learn from each other as a result, that would make a lot of sense.