Wow, strong ANTI-backpacking sentiments!
Is it the smell?

Did lots of backpacking style travel ... back to the early 70's. Criss crossed Mexico, Cent. & South America several times on buses trains, private vehicles and a few motorbikes.

I was lucky enough to be able to mix it up with occasional travel on a bike, haven't really done full back pack travel since early 1980's. All bikes! Like others, I've flown places as a back packer, got there and rented a bike.
Thailand, Cambodia, Vietnam. (only short visits)

Rode a Jawa 350 a bit in Mexixo, onto Guatemala and El Salvador. Another trip had a Honda 50 along mostly for Mexico. (attached to friend's camper). Did more of this in S. America.

But since late 80's all bike trips for me. I could go back to backpacking but it would be tough now ... I'm too accustom to all the advantages on being on the bike ... and too soft and too old to tough out backpacking. (like hiking around La Paz, Bolivia for two hours looking for a Hotel! all at 4000 meters)

Everything everyone says about the "freedom" with the bike is true ... and it feels GOOD to get back on a bike after riding in buses 12 hours a day. But it's amazing where you can get to on a bus if you inquire on routes.

Probably biggest PLUS to back packing was local contact and improved language skills. You had to learn ... or get your seat mate to TEACH YOU. (That's what I did)

I'd see groups of kids who never reach out, stay as a group, rarely talk or attempt to interact with locals unless forced to. But they have a ball anyway and they do what they do. So what. No law says you have to become a multi-cultural warrior. (although you'll be smarter and wiser if you are!)

The Ozzies and Brits were often poor with language in Latin America. I bailed several out of trouble (and jail) due to simple misunderstandings. So some pay off there I guess.

But often buses DO suck. Trains a bit better. I traveled thousands of miles in Peru' by train. The trip from Lima up to Huancayo was memorable, highest train ride in the world, passing over 17K ft. Took ages. A long tough ride on a bike back in those days.

Getting back on the bus was disheartening after riding, so I get what guys are whinging about. Also, older I get the harder the backpacking scene is to take. So I agree with those sentiments to some extent.

But backpacking also has it's "freedom's". No responsibility to maintain and repair a motorcycle. Some of the younger generation are woefully ignorant of even most basic maintenance/mechanical skills and some have no interest in learning. (my step son for example)

In USA most high schools don't offer Auto Shop like the old days. I learned so much there.

Backpacking also means no border hassles with TVIP's, insurance and dealing with whacked out crazy local traffic. No accidents, no hospitals and no ***** transito trying to impound your bike. (been there, done that)

That said, I've been in TWO pretty good bus accidents. One in Guatemala, another in Bolivia. Fist fight broke out at one of them.

Far as Gringo trail stuff goes ... many bikers follow the same path and end up in the same places along the ever widening Gringo Trail. Difference is, once you learn of better, less exploited places, you can jump on your bike and be there quick. Not always so easy juggling bus schedules and once you've paid your room, hard to get a refund. But a good backpacker will think and plan outside the box and OFF the Gringo trail. These skills transfer well to travel by bike.

Backpackers used to not be welcomed everywhere in S. America ... the unfounded fear of dirty, broke Hippies "invading" communities was strong, supported by right wing, US backed reactionary press and govts. ... moderated now I'm sure.

And even then, I was approached several times by very serious father's offering good money to marry their daughter and take her back to "Los Estados". This still goes on I hear.

Drugs were a BIG DEAL in the 70's ... many died from Cocaine abuse ... no wonder as it was SO CHEAP and plentiful.
I witnessed a lot of this. Backpackers were always targeted as suspects.
Now? I've no idea ... but would not surprise me. Funny, since back then it was nearly always local military or govt. officials doing the serious smuggling. (That is a FACT)

On my bike I never felt targeted or suspected despite a thousand military stops and searches.

But now, in Mexico, it's Speed that's killing kids ... and Speed users are often young Cartel killers by age 13. So ugly. Stay clear of that. Ruthless little bastards. Backpackers may be more likely to run into these scenes at bus stations where bikers may avoid it.