This is clearly a matter of personal opinion because a person’s stance on this issue is tied to their moral beliefs about the relative status of human beings and animals. There is no way to objectively prove how important animals are compared to humans. Therefore, this issue cannot be settled in an objective way.
If animals have no rights and no intrinsic value, then any experiments done on them are ethical. We think nothing of doing experiments on chemicals or on plants because we feel that these things are not valuable for their own sake; they are only valuable if they can help us. Therefore, we can do whatever we want to them.
If, by contrast, animals have just as many rights, and just as much intrinsic value as humans, no experiment could possibly be ethical if it would harm an animal in any way. We do not allow experimentation on human beings without their consent so we cannot justify experimenting on animals that cannot give consent.
My own view lies in between these polar opposites. I would argue that animals do have more intrinsic value than chemicals, but less than humans have. I would argue that experimentation on them is ethical when it is truly important for human beings. For example, I would willingly harm any number of animals to learn how to eradicate cancer, but I would not harm an animal to determine how to make a better lipstick.
Again, however, there is no way to objectively prove what the right attitude is on this issue.