Ah yes, the obligatory "lol just don't use $thing" response. Helps nobody, but I guess it lets you feel superior.
I hate Facebook as much as anyone, but in the real world people don't always have the luxury of getting to use whatever you consider morally correct. Especially with a messenger – depending on where you are, Whatsapp might just be what most people are using, and the people are the reason you would use a messenger in the first place.
People who say this in response to a request for help should just be perma-banned. Just get rid of them flat out. It’s the sure sign that someone is a total buffoon and will only ever make the place worse.
I think there's value in pushback against popular but problematic software. Some people just don't realize that, for example, WhatsApp is owned entirely by Meta and is known to collaborate with law enforcement, which are two facts that entirely undermine its main selling point.
Yes and if someone was looking for advice in general then it would be appropriate. Or if this were a security sub. Or, if you had a solution available and included a warning parenthetically as a courtesy.
But responding to a request for help with telling the person they should not do what they want to do is a tired old obnoxious cliché and nobody appreciates it. It’s universally hated.
Privacy is not the point of OP's question. A good answer would've been saying there is no WhatsApp client for Linux, and then (optionally) explaining that Signal has a desktop client and is a also privacy-respecting choice. Insulting OP by stating "You should not use this or that" is such a StackOverflow thing and helps nobody.
Edit: Just to make sure: I've never used WhatsApp and never will use it.