I agree it is unwise to connect batteries in Parallell for the reasons you state. You may well be able to use power diodes with SLA and NiMh batteries but this should not be used with LiPo's as their characteristics require close attention to each cells voltage.
Overcharging or discharging any one cell can cause irreversible damage and in the worst case destruction of the cell and battery pack.
LiPo's are available in very high capacitys and unless you are into high speed endurance racing I doubt if you would not be able to source a battery suitable for most sport usage.
Used correctly LiPo's are safe for model use but I agree you should be aware of the issuses should you not follow the correct procedures when using or charging.