Diesels are dirty
To make such an assertion it is only fair to examine (judge) diesel engines relative to their time period. The use of diesel engines, specifically in the pickup truck segment, did not become "mainstream" until the mid-1990s, despite Ford and GM introducing engines in the early 1980s. One could argue that the early diesels produced excessive emissions, however there were no regulations in place and a lack of knowledge (or acknowledgment) of the seriousness of exhaust emissions from internal combustion engines in general.
Modern diesel engines, however, are extremely clean in comparison and utilize a range of specialized aftertreatment devices to ensure that the tailpipe emissions of a diesel engine are no more worrisome than that of a gasoline engine. In fact, the diesel particulate filters (DPF) and selective catalytic reduction (SCR) systems on modern diesel powered vehicles minimize particulate (soot) and nitrous oxide emissions.
Diesel engines get bad fuel economy
For one reason or another, the term "diesel" has yet to become synonymous with fuel economy. However, the diesel cycle has a significantly higher thermal efficiency than the Otto cycle, the principles of which describe internal combustion engines using gasoline. Furthermore, diesel fuel has a greater energy content per volumetric unit than gasoline, contributing to even greater fuel savings. More energy per gallon of fuel AND an inherently greater thermal efficiency? This myth could not be any further from the truth.
Diesels are slow/sluggish
This claim could not be more of a fallacy and is likely derived from the fact that people immediately associate a diesel engine with towing a trailer. As a result, it is imprinted in your brain that that slow moving vehicle hauling a trailer has a diesel engine and therefore diesel powered vehicles must be slow. In reality, the performance of diesel engines is in many instances superior to that of comparable gas vehicles. This is primarily do to the fact that a diesel engine produces higher peak torque than a comparable gas engine, produces this torque at relatively low engine speeds, and maintains peak torque over a broader RPM range. Diesel trucks in particular have relatively high horsepower and torque ratings, but may not necessarily be "fast" do to the weight of the vehicle. If you drive a modern diesel car or truck you'll be pleasantly surprised with the performance characteristics and even more thrilled with the fuel economy.
Diesel engines are noisy
This is actually somewhat of a fact unless you focus on the last 7 to 10 years. Diesel engines exhibit an inherent "cackle" during injection events and although turbochargers tend to help muffle exhaust noise, the engine itself can make quite the racket. However, noise, vibration, and harshness (NVH) has been an important subject for engineers designing modern diesel engines. The result is diesel engines that are extremely quiet, both from the tailpipe and engine bay. You will have no problem holding a conversation across the hood of a modern turbodiesel.
Diesel engines won't start in cold weather
A properly maintained diesel engine will start in cold weather with minimal effort. While a diesel engine relies on hot compressed air in the cylinder to auto-ignite fuel, cold temperatures do not inhibit the combustion process entirely. Diesel engines do, however, face different challenges than gasoline engines in cold weather. Thus, all diesel engines have some form of starting aid (typically glow plugs or a similar device) that help heat the incoming air charge while the engine is cold. Most diesel engines also have block heaters which, when used accordingly, help engines start in even sub-zero temperatures. An additional cold weather challenge of diesel engines is that diesel fuel has a tendency to thicken and gel in cold weather. Specific anti-gel fuel additives maintain the consistency of fuel and eliminate this problem altogether.
Diesel engines have a higher cost of ownership
Diesel engines may have a higher cost of ownership than gasoline engines, just as gasoline engines may have a higher cost of ownership than diesel engines - the comparison isn't always apples for apples. It depends greatly on the vehicle type, what the vehicle is to be used for, and how long the vehicle is to be owned before selling or retiring. The service costs of diesel engines are typically more expensive, but this additional expense may be offset by fuel savings. One must also consider the fact that diesel powered vehicles hold a higher resale than those equipped with gasoline engines. Do the math before you pass up on that highly efficient turbodiesel.
Diesel fuel is hard to find
Diesel fuel may not be readily available at every fuel station, however it is available in most, if not all localities across the U.S.A. The root of this myth is that many people don't see diesel fuel pumps when they refuel their vehicle as it is commonplace for stations to have less diesel fuel pumps than gasoline pumps. It is not, however, difficult to find a diesel fuel station.
Diesels can run off vegetable oil
Diesel engines can run using biodiesel, a derivative of vegetable or other oils, but you cannot dump straight vegetable oil from the deep fryer into your fuel tank. Biodiesel is the result of refining various oils and/or animal fats and separating their constituents. All glycerin, contaminants, and any fine debris is separated, removed, and/or filtered from the oil stock prior to being regarded as fuel grade biodiesel.
Diesel engines don't perform well at high altitude
A turbocharged diesel engine performs BETTER at high altitude than a naturally aspirated gasoline engine. In fact, many diesel engines were engineered as naturally aspirated engines and turbochargers were later integrated to combat the loss of power experienced as altitude increased. Air becomes less dense as altitude increases, thus engines don't receive as much air and performance suffers. However, a turbocharger helps compensate for this phenomenon. Power loss do to altitude changes is therefore substantially lower in turbodiesels than any other engine.