Mosquitoes need to go and so do cockroaches they carry lots of illnesses and hurt people. The world would be better without those pests. Rats and mice are also a nuisance and cause damage to food.
However animals eat them in wild and are part of an ecosystem.
Then finally there are dogs and cats. As much as I don't like sterilization on sentient creature a lot of dogs and cats suffer. Litters of babies will die and those who survive will repeat the same suffering of being hungry and dying in the streets. I can't rescue every stray dog I see when the local street dog will go and make another litter, And I see dogs who have not eaten.
This is indicative of some very scary ideas that seem to exist amongst self proclaimed 'animal lovers'. On one hand they claim the animals should have rights and dignity, Similar to that of humans. . . They claim that animals can feel complex feelings like love, Depression, Etc.
Ironically however, This same school of people think that maiming animals is a way to express their love for them. They have twisted this practice into a way of loving and protecting their animal. . . As if they are giving it a better life as an eunuch under their command.
I say, Which is it? If you can justify performing such a thing on a species, How can we then also say that that species deserves rights to life, Or rights against torture and the like? How can one say they are actually loving that thing? What does this say about their definition of love? Some people out there truly believe they love (or can love) animals more than humans. What does this say about that level of love? Isn't it a contradiction to say the animal is capable of such levels of love, And that you love them, If the animal isn't capable feeling hurt by someone taking its natural given means of reproduction away from it? Doesn't this also put these persons humanity towards others into question? That they could perform it to something they 'love', Then why would they not also condone doing it to you against your will? (Someone they oftentimes care less about)