This is a difficult subject because it cannot be proven in the same way 
quantum mechanics or the laws of physics are proven. Our own sexuality 
and personality tend to give us a bias in interpreting 
words and pictures.     However, "to the impure, all things are impure" 
is an old saying which has some truth to it.   A good writer acknowledges 
and portrays the thoughts and actions of the innocent and the wicked, while 
some readers only see the wicked.  

Eyeglasses come in many colors. 

In my opinion (as an artist) drawings require so much time and 
concentration that they reflect the intentions of the artist, as compared 
with a snapshot.   Some of the most lewd strokes on paper belong to a 
writer of "children's books" who is very popular.

Rumiko Takahashi-sama's drawings are not lewd.  They are clean, expressive, 
even downright cute and wholesome.  

Love is not lust.  Feelings of kindness and willingness to sacrifice 
a lot for another's happiness is not lust.

Lust is  ...  well, that's what lemon fanfics are for.   And some of them 
are very well written.  They should be clearly labeled (and I believe all 
of them are) so that those who do not want them will not be surprised and 
those who do enjoy them can gain ready access to their favorite reading 
material.

Also, lust tends to be associated with a "more the merrier" rather than 
"only one in the world" preference.  And perhaps a "not to worry" 
attitude with attaining certain physical sensations being the most important 
goal.    

In the manga (Rumiko Takahashi-sama's creation), there are many 
opportunities for (P-chan) or (Ryoga) to take advantage of.  When the 
girls chasing Happosai run over Ryoga, then get off him leaving Akane 
still on his back, Ryoga has his eyes closed as he waves a greeting to
Akane.  He does not look up.

When Ranma pitches P-chan into the girl's locker room to "create a 
diversion",  P-chan immediately flips around with his back to the 
half-dressed girls and blushes with embarrassment.   And when Akane grabs 
him and quickly squeezes him, he (has a nosebleed) and faints.

Also, Ryoga is portrayed consistently by Takahashi-sama as being 
exceedingly shy around girls.  Shy people may become less shy as they 
grow older, but they do not suddenly become lewd, crude, lustful, or 
hentai despite the situation.   It may be convenient for a writer of 
fanfics to alter the personality or attitudes of the characters, but the 
manga consistently portrays Ryoga as very self conscious.

He has high morals, always helping the weak and helpless.  He does not 
wish to know his opponents weakness so as to take unfair advantage,

He idealizes and adores Akane, placing her on a pedestal.  He would never 
do anything to make her repulsed by him, but he does love her and wants 
to be near her and to be loved by her, even if it is only as a pet.  This 
is his need to be loved, which all human beings have, but he expresses it 
towards Akane in a very platonic manner while he is P-chan, and tries 
very hard to let her know how he feels about her when he is Ryoga. 
When Ranma (as Ryoga's "sister" Yoiko interferes with Ryoga's chance to 
be alone with Akane, Ryoga only feels sympathy for her, and  guilt for 
himself for having ignored her loneliness (after all, everyone else in 
the family was always away from home, lost).  

Unfortunately, because of his extreme shyness, his wanting to be sure he 
won't be rejected (that is, being assured she really likes him), and 
Ranma's aggressive ways of foiling Ryoga's plans (because Akane does like 
Ryoga, if only as a friend, so Ryoga is Ranma's only rival for Akane's 
affections), Ryoga is not likely to ever be Akane's boyfriend.

It is normal and natural to have hormones that affect blood pressure 
(among other things).  That is not lust.

His inability to get to a specific location keeps him from the 
companionship of others and is the primary reason for his unhappiness.  
He would like nothing better than to be near someone he loved and to be 
loved in return.   He never attempts to touch or even look at any of the 
females in Ranma 1/2.  He won't fight a girl (except Ranma-chan, whom he 
always thinks of as male Ranma, his rival.)

As a character flaw, he never looks closely at girls 
and never expects them to be deceiving him, so Ranma as Ranma-chan can 
easily fool him when no one else (especially Akane) is fooled.  

Buy the Japanese manga (get a magnifying glass to see the artwork 
clearly), wait for Viz to translate and publish comics in English, 
and/or buy the Graphic Novels and decide for yourself how Takahashi-sama's
characters are.  This is the best series available! (IMHO)

Enjoy the anime, remembering the names on the cover whose ideas and 
attitudes are present in the final product.

Read fanfiction, (there are some great writers), remembering each work is 
the product of the writer's own imagination even if the names of the 
characters are the same in each story.

Gomen nasai.   I promise to NEVER write so much in any one post again!
Let the flames begin.  I have nothing to lose.