In Emunot V'Deiot 3:9 R. Saadia Gaon explains that prior to the priesthood of Aaron and his sons, there were always specific people appointed to perform sacrificial services:
The third [problem is presented by] the fact that God commanded all men to offer up sacrifices and then forbade such activities to everyone except Aaron and his children. But this, ...
In moderation meat isn't bad for you.
In this article on the issue, the bottom line is:
Unprocessed and properly cooked meat has many nutrients and may have some health benefits. If you enjoy eating meat, there is no compelling health or nutritional reason to stop.
God wants us to enjoy in a reasonable fashion!
Rav Hirsch explains this at length in Beraishis 4:3-6
3 Now it came to pass at the end of days, that Cain brought of the
fruit of the soil an offering to the Lord.
4 And Abel he too brought of the firstborn of his flocks and of their
fattest, and the Lord turned to Abel and to his offering.
5 But to Cain and to his offering He did not turn, ...