Sorry, you just asserted that a "species" is defined by "individuals that can interbreed to produce fertile offspring". That's a high school biology definition.
First of all, what do you mean individuals that can interbreed? I've got two male dogs, they can't have puppies - so what, are they different species? My cat's fixed and she can't have kittens - so is she not a cat anymore? Not to mention humans undergo menopause; are they not human any more? Do you tie someone's humanity to their ability to have children? Do you want to rape babies to see if they're fertile, you creepy sick fuck, or are you trying to justify treating them inhumanely because they don't count as humans yet? Are you trying to justify genociding babies through your bioessentialist hate rhetoric, since they can't interbreed with humans to produce fertile offspring so are animals you can hunt for sport? Are you literally trying to enact violence against babies??
Not to mention this whole fertile offspring bullshit. People say horses and donkeys are different species, and mules are just "infertile hybrids". Let me show you something that will blow your tiny mind.

Sometimes mules can get pregnant!!!!! I know your high school teacher told you "they have an odd number of chromosomes so are infertile because they can't viably produce haploid cells through meiosis" but how do you even know what chromosomes an organism has? Are you walking around karyotyping everything you see?! Plus there's actual scientific consensus of something - you wouldn't know about it because you're so stupid - called "behavioural speciation", where like fruit flies undergo prezygotic reproductive isolation because they don't understand each other's mating behaviours, but can produce fertile offspring if you do like fruit fly IVF. So like are they different species or the same species!?
What about ring species?

Is the herring gull one species or multiple different species? You're just going to arbitrarily categorise them as such? You can't just draw hard lines through reality because it makes you more comfortable.
You're trying to go back to some stupid regressive version of the past that you've imagined where "everyone knew what a species was".

People used to think glass eels, elvers, yellow eels and silver eels were all different species - it wasn't until the 1890s that people realised those were life stages of the European Eel! And people thought the Portugese Man O'War is a "species" when it's actually a plural system of commensal organisms. You want to erase their truth. You literally want to live like Medieval people who thought sheep could grow on trees, and that's so... sad for you. That's not it, chief.
Not to mention this weird fixation you have about "interbreeding". Are you just assuming that everything fucks like some 1950s "Leave It To Beaver" charmed circle married white Christian couple? What about the lesbian lizards?

There's actually lots of forms of reproduction. All the male lizards went extinct but the lesbian lizards are still reproducing through parthenogenesis. But they literally can't interbreed as a result. So what, they're not a species? They're not alive? You're free to put them in the microwave for your sick kicks because according to you they don't count as alive? You're a fucking zoosadist trying to justify your perverted behaviour. Not to mention double fertilisation of - especially - wind pollinated plants?

See? Sex isn't what you think it is, what you call interbreeding isn't some simple straightforward thing. I bet you think it's justified to deforest the Amazon because those plants don't count as interbreeding in your narrow definition of the world. Not to mention all commercially grown bananas are infertile clones incapable of breeding... so do you want to go arresting people who eat bananas, you fuck?
Plus what if in the future they had advanced gene therapy technology that meant you could become your fursona, and then you could interbreed with foxes to produce fertile offspring? Would you still say they're a different species then, or can tiny mind not comprehend that the world doesn't revolve around making bigots feel comfortable? What if we found aliens like the Asari from Mass Effect who can interbreed to produce fertile offspring with any species!? You call me a special snowflake but you're the one lashing out because your fee-fees got hurt.
All I want to do is marry this ram that I bought off a farmer. But your assertion "that's a fucking different species, you can't marry it, also it's not even a ram, it's a sheep" - why do you hate love? Why are you so concerned about controlling other people when we just want to live? We've just established that there's no objective thing as a species, you can't define a species in a way that includes all biological situations without excluding any biological edge cases - so it's a social construct, THEREFORE the only thing that matters is that I define him as a human man.
ANYWAY what do you even mean by he's "biologically a different species"? He's biologically my species, because he's my species since I say so, and he's not a robot so he's biological. How would you even check what biological species someone is? Do you want to set up rape stations so you can rape animals all day to see if they're fertile for you, you freak? Your psychosexual obsession with animal genitals is so repulsive. It is none of your business what's in an organism's reproductive system.
This is what their arguments about biological sex sound like.
Including scientific inaccuracies, the Herring Gull Complex is no longer considered to be an example of a ring species. I had to sit through three hours of that insanity yesterday while pretending to politely agree and it really was all like this.