I'm pretty sure the fare gates aren't replacing conductors checking tickets on the trains, it's just a second check, and requires everyone going to and from North Station to have a ticket. I assume on Septa there's no penalty if you just tap on and then tap off at your origin and destination and the conductor doesn't make it to you during your ride. There collecting and checking fares for passengers not going to and from Center City.
Their multiple Metro systems, where you have to tap a ticket to both enter and leave the system on a fare gate, Washington DC, and BART are clear examples, it doesn't violate fire codes.
NYCs emergency exit gates and didn't have slam bars until the late 2000s (
Lawrence Street, now part of Jay Street-Metrotech got the first in 2006) and were controlled from the token booth. Before the emergency exit gates that had super obnoxious alarms when the passenger operated bars were added and you were getting off the subway with a bicycle or stroller for example, you needed to get the attention of the token booth to leave the subway, some of them had a button to call the token booth, who would then open the "Special Entry gate" as they were signed for you.
The subway basically came full circle, before the early 1990s when all the stations had new electronic turnstiles installed for MetroCard, many stations had slam gates, a gate that exiting passengers pushed open to leave the subway next to the turnstiles. I remember at my childhood station, 181 Street, there were originally two slam gates on each side of the turnstiles, one was replaced by a special entry gate, the other just became a fence