How do Catholics feel about their church invalidating baptisms due to a trivial grammatical choice?

The article speaks for itself. The prescribed liturgical form for all such things belongs to the whole Church; not any particular individual or little group, who might choose to revise or subvert it, strictly for their own purposes.

I am tired of the ignorant attacking the RCC,  nor am I one

I'd suppose that most of them are supportive of it

since the ones using the alternate formula are doing so without permission.

That is: they are performing

what is for Catholics

an extremely important religious ritual

in a manner that is unauthorized.

Catholics are pretty big on tradition when it comes to religious matters

and bucking established ritual proceedings without permission is likely to be viewed as rather cavalier, bordering on the heretical.

NO Christian would call that difference "trivial."  Your ignorance is showing.

Christians worship God as Father, Son, and Holy Spirit.  For those calling themselves Christian but not denying the Trinity, Christianity is their "philosophy" -- not their religion.