Well, since you have brought the subject up, there is a stark difference in the condition of LA County (or even the tourist destinations of North Carolina, Virginia, Florida et al) beaches and those of Thailand. There is no trash on the US beaches. They have garbage cans regularly spaced and people have been taught not to litter. There are also restrooms on their beaches. My walk on the Hua Hin beach this afternoon was distinguished by dead fish, horse manure, plastic cups/containers/straws and plastic bottles. You don't see that in the US beach locations you were mentioning.
Yes, there is a hygiene problem with parts of LA. Most people don't visit skid row so don't have to deal with it. The city does hose the place down with disinfectant. Yes, the vagrants and mentally ill cause a mess in LA and elsewhere however, they are not destroying public beaches, not even in Venice, CA. India doesn't clean anything period. It is a nation where people throw their trash over a neighbor's wall and think nothing of it.
And please don't mention the quality of Thailand's beach water. When is the last time the government released a water quality reading? There is a reason why they won't do it. You need only look at Patong Bay to understand why.