I better respond one at a time George:
1) "I read some place that undercharging a battery is just as bad as overcharging."
There's some truth in that George. BOTH are bad on a battery. Overcharging can indeed ruin a battery as well as letting it set fully uncharged for a long period.
2) "A solar charger won't charge a battery very fast."
NOT TRUE it depends on how many watts the Solar Charging system is and the quality of the Solar Charge Controller. A 20 watt system cant charge as fast as say a 400 watt system now can it!!!!!
3) One should bring the battery up to full charge asap.
SORT OF, HOWEVER, you don't want to charge it so fast and at such a high rate she boils over or outgasses excessive or damages the plates!!!!!
Its best to utilize a Smart Three Stage Charger, it will first use a relatively faster BULK CHARGE (may be as high as 14+ volts) to initially bring it up,,,,,,,, Then slow down the charge rate to ABSORPTION CHARGE (may be around say 13.6 volts),,,,,,,,,,,,Then settle down for a maintenace FLOAT CHARGE LEVEL (may be like 13.2 volts)
4) "Solar can't do that."
IT CERTAINLY CAN with the likes of an MPPT Solar Charge Controller like I have!!!!!!! My MPPT Solar Charge Controller allows a higher charge rate initially, and as the batteries become charged the charge slows down
IT SOUNDS LIKE YOURE THINKING OF AN OPEN UNREGULATED SOLAR PANEL GEORGE??? That would run wide open all the time with no smart regulation and yes it could overcharge a battery
5) I would recommend a charger that not only charges a battery, it desulfates it too.
YOU GOT THAT ONE RIGHT GEORGE
My Smart FOUR STAGE charger has BULK,,,,,,,ABSORPTION,,,,,,,,FLOAT,,,,,,,,,AND DESULFATION CYCLES
Okay, my answer was to his question ONLY and I cant take the time to write an entire thesis here on Solar Charging, so I urge you and the other the readers to go research and study up on the the topic ITS FUN AND FASCINATING.
I ONLY covered a few basics, so dont get bent out of shape, its NOT perfect, just a primer for those interested to go study more
HOWEVER I did address your 5 topics
John T