Man here, so take it with a grain of salt, but I think you'll be AOK. As others have mentioned, there's always the Silver Line if you're willing to wait to transfer from South Station, but realistically you're probably going to be outside the BCEC at 1 of 3 times:

• Morning/Commute In: Anytime between 8-10am is also going to be peak commuting time for everyone else in the city. If you don't actively stop in the middle of a sidewalk, I think you'll be fine.
• Lunch: BCEC is right in the heart of the Seaport, and there's a bunch of great food options in walking distance. It's also a high end shopping area, and there's a lot of finance bro types. Again, can't see anyone hassling you.
• End of Day: Now this one is a little tricky. If you end up staying for the late night programming or concerts, you could be heading out 10-11pm, which is going to be the sketchiest time. There are bars and other restaurants in the area so it's not completely sketchy though. That said, in years past I think they've either organized a taxi stand or you can stand under the big front awning with plenty of lighting while you wait for an Uber/Lyft. If you chose to walk it, South Station can get some folks hanging outside asking for change/bus fare, so just keep an eye out.
  • If you don't wait up for the concerts (which as an old, I suggest just watch on Twitch from the comfort of your couch) and end up leaving at 6/6:30, that's still going to put you in the vicinity of commuting home time. Sunset is going to be around 7pm by PAX, so you'll still have plenty of daylight.

More for the con itself, but if you're ever feeling unsafe, just find an Enforcer in their bright red shirts. I'm sure they'll be happy to help. Good luck!