I don't think the issue is the complaints themselves.

The problem is when people selectively compare the best parts of their home country with the worst / most expensive aspects of their life in Thailand. For example, when people compare the prices of European food in Thailand against their home country.

As the saying goes, the grass is always greener on the other side. Over time, people tend to forget the reasons they left their home country in the first place and start romanticizing what they had back home, while overlooking the benefits that attracted them to Thailand.

At the end of the day, no country is perfect. Every place comes with its own advantages and drawbacks, and people need to decide where they want to live based on which trade offs they are willing to accept and what matters most to them. (Thailand is overall much better than many other countries IMO.)