Zealotry will do less damage to your career than epistemic closure.
If you had to choose one of two faults: Nothing But Microsoft OR Anything But Microsoft -- you're going to be better off as an ABMer since (theoretically) your ecosystem of options is MUCH larger. Rejecting Microsoft still leaves you with several other marketable options. Rejecting everything that isn't Microsoft leaves you completely at the mercy of a single platform that you have no control over (and if you did have control over it, it still wouldn't be ideal)
You're making the assumption that MS is the only target, it's not. The reason it's so destructive is because you eliminate certain options based on emotion rather than reason.
So on one hand you're dealing with a fanatic that only sees black and white, and the other you're dealing with apathy. Not exactly good options.
If you had to choose one of two faults: Nothing But Microsoft OR Anything But Microsoft -- you're going to be better off as an ABMer since (theoretically) your ecosystem of options is MUCH larger. Rejecting Microsoft still leaves you with several other marketable options. Rejecting everything that isn't Microsoft leaves you completely at the mercy of a single platform that you have no control over (and if you did have control over it, it still wouldn't be ideal)