Still don't understand why neutering your dog is an issue
It needn't be. Some dogs need to be neutered for medical reasons, some for social ones (they're very, very "humpy"), some as a way of preventing unwanted puppies etc - I'm sure that there are more.
The "unwanted puppies" reason is the one that most vets/ rescues quote. However there are many equally good reasons for leaving a dog entire (though not a bitch - she's the one who has the puppies after all, and bitches can get mammary tumours, ovarian and uterine cancers and pyometra if they aren't spayed.) - and I wouldn't have it done (with the knowledge I have now) just as a matter of course which it's pretty much become - it's not "if" you get your dog neutered, but "when" these days.
And advantage (not to the male dog's owner though) of all dogs not required for breeding being neutered is that it greatly reduces the risks to bitches which are high risk for surgery and can't be spayed.
No-one has to spay a bitch, either, but you need to be sure you can keep her in if you don't want her to have puppies (and she will try to get out - she'll get desperate!). If your bitch is accidentally mated it will cost you £200+ for a mis-mate jab to prevent conception (and it's putting a lot of very powerful hormones mother body). Of course you could let her have her puppies and then sell them/ give them away - but that it a HUGE responsibility if you are a caring owner - and if you don't know which dog has "caught" her (and there could be several) you don't know if the puppies will be too large for her to whelp safely. An emergency caesarion (£1,000+ - depends on size of dog, time of day/night, any complications ) may be necessary, and even if your bitch has an easy whelping, she can develop eclampsia, which can occur very suddenly, with little or no warning and is very often fatal.
It isn't always all beer and skittles.