1.5g/lb (3.3g/kg) is considered by many in the weight training communities to be way overkill, and potentially hard on your kidneys.
source - https://bayesianbodybuilding.com/the-myth-of-1glb-optimal-pr...
Eating more than 2.6 g/kg (1.18 g/lb) is probably not going to lead to greater muscle gains, but it can minimize fat gains when “bulking” — i.e., when eating above maintenance in order to gain (muscle) weight.
There doesn't seem to be a lot of evidence for the kidney thing as long as you don't dramatically increase protein suddenly: https://examine.com/nutrition/can-eating-too-much-protein-be...
Personally, a simple flat 100g seems both a reasonable & attainable goal for most regular people building muscle without requiring exceptional diets (here I fall back on naturalism- I cannot believe that exceptional diets are required to get fit). You can easily hit that number with 1/4-1/3lb of meat a day plus whole grains and vegetables.
Since higher protein intakes seem to have no negative effects in healthy people, one may want to err toward the higher amounts.
I haven't seen anything over 3.3g/kg recommended anywhere, and most people seem to recommend 1.4-2g/kg as a good baseline amount. The ISSN recommends this (see here: http://stevenlow.org/issn-position-statements-protein-and-ex...), however the ISSN does recommend higher amounts when losing weight:
Higher protein intakes (2.3–3.1 g/kg/d) may be needed to maximize the retention of lean body mass in resistance-trained subjects during hypocaloric periods.
Of course, none of this is required to get fit - you don't need to do the optimal thing to get a basic result. But you'll definitely gain lean mass faster if you do follow this. Those recommendations for weight gain (say 2g/kg with a caloric surplus) is easy to achieve with no supplementation and normal food, at least for an omnivore - vegans may have to work harder to get there.
Is there data for that?
IIRC, for healthy kidneys this amount should not be an issue, slightly more per lb shouldn't be either.
I'm not sure what weight training communities you refer to, but in bodybuilding and strength circles amounts that high and higher aren't often considered "way overkill".
Anywhere between 0.75-1.25g/lb is where I shoot for, depending on my goals. But I have gone higher than 2g/lb for extended periods of time in the past
High protein, low fat, low carb, low protein, high carb, high fat- collectively we've tried them all through one fad or another.
Currently IMO we're in a blowback period where we are seeing high carb is not panning out and many people are still afraid of fat, so protein is the next savior in line.
For what exactly? It pans out just fine for various things, or are you specifically talking about weight loss?