Pure cotton uses 50x more water / pesticides and associated damage to water table. Sure it's more transient but we know pesticides is bad, we _think_ microplastics is bad, but only in the vague, it upsets the environment in some systemic way, not heavy water and pesticide use wall definitely fuck up some local balance way.

Highend synthetic tech fabric will mechanically outlast a cotton shirt. This not even debatable outside of anecdotes. We KNOW with certainty material properties, synthetics can be significantly - not even in the same realm - more hard wearing than the best cotton. Manufactures just cheap out, like they do cheap cotton.