If you look at what the experts say in the article, I don't think any of them say anything that means "Linux is fast, flexible and free. That comes with a security cost". In fact, I'm not sure the author of the article is even saying that, although they're certainly trying to cash in on some fear. This title is misleading.

Ultimately, I think the message of this article, that Linux out of the box isn't inherently secure, and the culture around Linux needs more focus on security, is true. But it's also being said in a vacuum, with no comparison to other platforms. Certainly the experts in question were right to have concerns about Linux security, but I'd put bet money on the assertion that they have even greater concerns about, say, Windows.

And finally, some of the problems being blamed on Linux are actually problems with the tooling around Linux and the platforms Linux is being run on. Android is inherently always going to be insecure as long as it's running with GSM, which is fundamentally broken. Heartbleed was an OpenSSL bug. And Linus is absolutely right that if you are running Linux in a nuclear power plant, you absolutely shouldn't connect it to the internet.