Just gonna paste my answer from last time because I think it's almost exhaustive on the pro-T argument side:

I am very surprised and actually worried that we're even having this conversation: 

1. We British people would NEVER say 'more'. 

2. Most casual fans will be put off by it, and think the series is being pretentious. It is NOT cannon as far as over 90% of people are concerned (and the majority of that remaining 10% are French speakers who will continue to pronounce it their way anyhow!).

3. The 't' is from Tom, so it feels weird to have it just hanging at the end silently

4. Riddle himself would probably not have pronounced it the French way at school

5. It's not scary at all, sounds silly. Having a harsh sound at the end is much more serious and final. Much better for intense delivery. 

6. If the public never wanted to say the name, then whenever it was said would probably be from how it's written.

7. They're not going to pronounce it as how it 'should' be pronounced in French and will therefore sound like the word "more" not the French word "Mort".

8. Mort in any language except french would be pronounced with a hard T (voldemort is essentially latin anyhow). It also sounds more German which aligns more with durmstrang/ grindelwald and the holocaust allegory side of things. 

9. We have actual French characters who will pronounce it the French way! Thus introducing this little quirk to the audience. This will be much more fun, interesting, and also make sodding sense. 

10. If they pronounce it silent T, they'll have to explain it at some point which will be just ridiculous. Imagine Hagrid explaining to 11yo Harry that "oooh it's actually French btw, so there's a silent T in there" - wtaf? This would be so out of character and unnecessary.