That's just not true. I love how everyone becomes an expert when it's time for a debate.
Microsoft extensively uses open source software. Their lawyers, just like any big company, are fiercely protective of when and where each license can be used. They won't use viral licenses (GPL) in software where the source can't be released, but we will use it in places where the viral-ness can be avoided. BSD, MIT, ASL2 are used extensively throughout Microsoft, there's no restriction on using those licenses other than releasing information that you're using them. (Some other licenses like EPL or MPL are verboten because they have patentability implications, despite not needing to release source code.)
Source: Am a microsoft employee who deals with open source permissioning.