I know of one veteran domainer who always advises new domainers to desist from new gTLDs. He does it politely and with facts. He always says something like “I like to look after the little guy”. I listened to him and started buying more .COMs.
Then there is a crowd of abusive domainers who are always bashing new gTLDs and abusing the “fools” who invest in them. To be honest, sometimes I find their comments a bit funny. I don’t think they are driven by “concern” or feel threatened. Some people just like to bash what they don’t like and they can be quite virulent. Many of these guys assume people who buy new gTLDs are "anti-dotCOM"; no we aren't. We also buy lots of .COMs. Just spreading our risks and we aren't afraid to try out something new.
I don’t think new gTLDs threaten .COMs. I have studied sales figures for some of the top new tlds and the sales are far between and really low for premium domain names. The best investment is still .COM.
However, when I find a great new gTLD, I always snap them ASAP!
Some of my recent newgTLD acquisitions:-
Altright.men
Careers.men
Snuggle.shop
Antonio.life
Screwing.men
Quadcopter.guide
Wales.world
Glasgow.world
I welcome reasonable offers from fellow new gTLD lovers