The Uk needs younger workers, and immigrants supply that need. The economy has always benefitted from influxes of immigrants.

The fuss about illegal immigrants is that the government has no control over them. Obviously, they do not want thousands of non-qualified workers flooding into the UK, they want people with some skills, like nurses, carpenters etc

Thailand, on the other hand, has plenty of younger citizens, has no need for foreigners without some special skills, so is not welcoming.

Making comparisons between Thailand and the west is just a waste of time, they are totally different types of economies and it follows that foreigners are also treated differently. Having said that, the Thais could show a little more compassion to those immigrants who are married to Thais and wish to live their lives in Thailand without bureaucracy chasing them.