When has open sourcing your business's core software not been a risky strategy?
If you are a software as a product company and you open source your software, someone else may put it into a box and sell it beside you.
If you are a software as a business process company and you open source your software, some else may build into their business and compete against you in whatever your marketable output is.
If you are a software as a service company, and you open source your software, someone may build a service that is remarkably similar to yours.
Open source is great for things your company depends on --- maybe you get community improvements, and you can build and change it how you like; but if the core of your business is open source, that's a choice that makes it very easy for competition to form. OTOH, if you want to build something that other companies depend on, and there's open source alternatives, it's going to be hard going; I wouldn't use a closed source web server or database server or search engine, given there are good open source options; although maybe if those options don't work out, I'd consider a closed source vendor.