bats are birds because they fly and look like birds.
Bats are rodents. In fact bats in no way look like birds, even at a distance it's pathetically easy to distinguish at bat from a bird, bats wing structure and manner of flying is unlike any bird, neither is the way bats manuever or land. Bats don't glide like like birds do, in fact thats one of the telltale ways to identify a bat in midflight. Just because it might make sense to your limited intellect doesn't mean that it is therefore true, it means that you are wrong, uncurious, and willfully ignorant.
that's how we define things: by looking at them.
No, that is how a child who does not no better defines things. The rest of the civilized world has moved beyond defining things in such a manner.
ostriches are birds because they look like birds. flight is not necessary, if they are enough similar to a bird.
Ostriches are called birds, not just because they look similar, but because they exhibt physical features known to be unique to avians, such as hollow bones and feathers. They also exhibit genetic markers that are also unique and identify a species as avian.
i wouldn't call penguins birds because they look kinda weird. a little birdish, but not entirely birds. they are waterbirds.
There is no such thing as a "waterbird". Regardless of what you think about the appearence of penguins they are indisputibly avian in nature.
i think it's foolish to say that an animal is a different kind of animal just because it is warmblooded or coldblooded
Then you are wrong. The physical and genetic differences between the two types would render breeding between them to be impossible. Your lack of basic biological knowledge is shameful, this is stuff my children knew when they were still in elementary school. This is basic knowledge and for you to remain ignorant of it means that ignorance is quite likely willful and intentional.
or if it lays eggs instead of children
That makes a great difference.
because a normal person can't even notice if a creature has warm blood or not
A person can tell the difference between warm and cold blooded creatures by simple observation. There isn't any kind of incomprehensible test that can only be done by a scientist. In fact you can determine the difference using only sight or touch. It pathetically simple, even for someone as willfully ignorant as you.
only scientists can do that
Quit making excuses for your ignorance.
so scientists can have their definitions and we normal people have our own
Except thats not the way it works. Normal people and scientists tend to use the same definitions. Willfully ignorant and uncurious people like yourself make up definitions as they go along. In most cases you make up your own definitions because the alternative would mean that you would have to admit that part of the christian bible was incorrect.
Please don't insult the majority of non-scientists who are capable of understanding these differences and classifications that you willfully ignore.