That's a bit of a straw-man IMO. I'm sure there are plenty of people who are against it for that reason, but there are plenty who are like me, and don't want further role homogenization. The saying "If I wanted to DPS, I'd play a DPS." comes to mind. My concern is that if healers were given more damaging abilities, that will likely lead towards further role homogenization and removal of the trinity. If we're gonna go that route, I'd rather just play GW2. That game was designed around not having a full trinity and has a bad story (Thanks Dawntrail), but at least GW2 has good netcode.
This isn't to say IMO we can't have additional DPS abilities, but they should be subservient to healing. For example, someone mentioned an idea where Freecure procced a free GCD heal off of glare or random Dia ticks. Maybe Asylum could also have a damage tick added to it or Aetherial shift turns into a PVE Seraph Strike when targeting an enemy and consumes a lily. Obviously I'm just spitballing, but I think the priority should be to keep healers healing, and if we're gonna get more damage abilities, they should to facilitate our healing instead of just adding button bloat so we have more things to press.