please correct me Pets in city flats? Argue for or against.

Nowadays it is very common to meet people  walking with their pets, which are normally [1] dogs. Many years ago animals were at homes to served humans because we could eat them or use them to help us with our work working. Now it seems crazy because it has turned around and it is humans are who serve animals. 
To have a pet has is a lot of responsibility,  but it is sometimes can be good or bad it depends depending on the case situation. One advantage is that people who are alone can have a loyal friend, or an unsociable child  can be helped with pet therapy. On the another hand, to have a pet could  endanger your health if you are  allergic to them. In second place Secondly [2] it is now a problem that people sometimes  prefer pets to children child and it is not good for the country because we are growing up our population is getting older and we need young people in the society and families are very important. To conclude, pets are lovely but sometimes when people can not take care of them, or  when the pet has matured, they are abandoned in the streets. For this reason, we have to think about it this before bringing an animal into our flat.

[1] usually sounds better to the English ear, but normally is perfectly correct.

[2] In Spanish, you normally say "en primer lugar, en segundo lugar", but in English, we change this to firstly, secondly, etc. You use "in first place, in second place" to indicate who has won a sporting competition, for example.

Bravo, Christine!  You have done a very good job describing the pros and cons of pet ownership in city flats.