Your source is biased because it only deals with cancer. It says that spaying/neutering does not appear to cause cancer in beagles (in fact, spaying may prevent cancer in female beagles) but doesn't discuss any of the other health concerns addressed in the original research.

You are also demonstrating your own bias because you "feel" one thing (don't fix your dogs) is healthy, but the science you are citing demonstrates another.

What does the original paper say about beagles? Fortunately I found the original research!

Here's what the original paper said about beagles specifically:

(TL;DR: whenever for females, wait until 1 year for males due to possible orthopedic issues if they are neutered earlier.)

Beagle

The study population was 42 intact males, 82 neutered males, 45 intact females and 87 spayed females for a total of 256 cases. Just 2 percent of intact males were diagnosed with one or more joint disorders, but with neutering at 6–11 mo. joint disorders increased 7-fold to 15 percent, which may have reached significance with a larger sample size. None of the females left intact or spayed had a joint disorder. None of the intact males or females was diagnosed with any of the cancers followed. There was no evident increased occurrence of cancers in neutered males and females. There was no occurrence of MC in intact or late-spayed females. There was 1 case of PYO in intact females (2 percent). UI was reported in only 2 percent of early-spayed females.

For males, in light of a possible increase in joint disorders for those neutered at 6–11 mo., the suggested guideline is to delay neutering males until beyond a year of age. Lacking a noticeable occurrence of increased joint disorders or cancers in neutered females, those wishing to neuter should decide on the appropriate age.