It is a great topic for an essay or speech. There are couple of things you can include in the speech, which I will mention here. One thing to keep in mind is, you don't need to say western culture is good or bad. The topic is not really to prove western culture is bad. Instead, your goal should be to prove how the imitation of the culture could be bad for you. Every country has their own culture and values. It may not fit well for people in other countries.
In your speech, you will have to look at various trends in your country, which are imitation of the western culture and explain how it is affecting the values in your country. You will have to project the culture and trends that are not really suitable for you but suits the western countries well. For example, consider the spending habits. In western countries, people do not save much for next generation, instead, they spend their earnings for their own comfortable life. That may not be the case in your country. In many countries like India, people save money for hard times and for next generation. The new generation seem to be interested imitating the west, you can say is not a good idea and could result in declining values.