Ok Deathstare I'll bite.
No, i would not quite fucking obviously, be distracted by a disabled person being sat next to me in the theatre, or any of the other irrelevant comparisons you made to a squawking baby.
However, if said disabled person had a condition which caused them to scream, moan in confusion, hand flap (as was the case with my ASD son, when he was a toddler) then i would not be happy, no.
Though I suspect it's a moot point as a large amount of theatres and cinemas now have set days for 'autism friendly' and 'disability friendly' screenings, so it's unlikely to happen.
If i had paid £100 a ticket to watch a play, I wouldn't be happy with any out-of-the-expected noise or distraction.
I wouldn't complain about the person, god no. But I would request the theatre reimburse me, or swap my tickets for a future date.
The Theatre is no place for a baby, ever- unless the show that's being performed is more The Gruffalo than The Tempest.