Too much of anything can be a bad thing, including Secularism.
That's a bit like saying that too much equality is a bad thing. Or too much fairness.
Not really.
But you can have to much equality to the point it can be a bad thing.
It's when people don't recognise individuality and are obsessed with everyone being the same.
Blimey, not only do you not understand secularism, but it appears you don't understand equality.
The whole point of equality is to support diversity (hence loads of departments in companies etc are called Equality and Diversity).
Equality means that people are treated equally and do not suffer discrimination regardless of their diverse characteristics where those characteristics aren't relevant to a job, receiving a service etc etc. So equality ensures that people can develop their diverse individuality safe in the knowledge that they won't suffer discrimination because of it.