Which, for 99.99999% of actual users will mean they are blocked. Digging around in the guts to enable "Developer mode", with all the scary consequences, is not something users will (or should have to) do.
If you do the right thing for your users first, this is what you do. You put user needs over developer needs.
There is a middle ground between letting any malware on the machine install whatever extensions it wants with no user consent, and banning users from installing extensions entirely.