I think this is partly downstream of how highly EA prioritizes intelligence and seeming thoughtful/careful. 

This comment made me wonder what type of norm you're asking about. From Wiktionary:

1. That which is normal or typical.
   1. Unemployment is the norm in this part of the country.
2. A rule that is imposed by regulations and/or socially enforced by members of a community.
   1. Not eating your children is just one of those societal norms.

On second thought, veganism maybe is neither 1. nor 2., at least this is what the EA survey found 5 years ago about the frequency of veganism and vegetarianism:

39% of the effective altruism population reported being vegan or vegetarian

Curious why you want to remove this norm. Is it because it makes it less appealing to people outside EA? It is because it gives appearance of being more precise but actually does not do better than using everyday phrases?

wow