It's really a matter of understanding why they say that, and then what you think of their reasoning.
Basically, the Catholic position is that the purpose of sex is to be a vehicle for reproduction. That's clearly true physiologically, if it weren't a reproductive act it wouldn't exist. They take the position that when sex is unhinged entirely from that purpose, and engaged in only for secondary reasons, it becomes disordered and can become a destructive force.
It's actually very similar to how they see something like gluttony. Eating is a very pleasurable thing, enjoying food is good, and often an important social activity. But its primary purpose is to maintain the physical needs of the body.
In this case what they would suggest is that we should enjoy food and it's social role, but regulate consumption within the boundaries of it's primary purpose - what the body needs. if we totally forget about the physical needs of the body, proper nutrition and such, you will get problems like obesity, unhealthy eating, diabetes, but also problems like the industrial food system, other kinds of disordered eating, creation of highly palatable but unhealthy processed food, factory farming, and so on.
Similarly for sex, they would say, sex is enjoyable and loving, but the way to keep it from becoming something negative is to regulate it within the bounds of it's primary purpose. Otherwise it can become something destructive.
The typical argument against that would probably be that we can regulate in less exacting ways. Maybe keep sex within marriage say, or keep an eye on how much crap food we eat. On hte other hand, it's hard not to see that society has issues with over-consumption of sex and and food, and also questionable forms of consumption. Boundaries aren't so easy to maintain when you try and construct them.