On here, people do seem to have lots of issues with it.
I'm friends with all my exes, because all my relationships start from and are based on friendship, so if I liked them enough to date them, then even if it turns out we aren't compatible, I will still like their company. And neither they nor I are arseholes, so the relationships haven't ended for negative reasons like cheating or abuse that would destroy a friendship.
I still go out to dinners and 121 events/socialising with them all. And to me it's a green flag if my partner also does with his exes. I don't want to date someone who has behaved negatively to previous partners, or who becomes bitter and angry at the end of a relationship (unless there is, exceptionally, a good reason for that).
And if there are trust issues in a relationship, that's what I think people ought to work on, rather than issuing bans or getting upset about it. If you feel adequately secure in the relationship, people meeting exes isn't threatening.
But I'm aware lots of people see things differently.