I realize this is a profit maker for Verizon, so there is no motivation to make the customers life easier here, but honesly this is irritating enough to drive me to another carrier.
On the contrary, Verizon Wireless offers various ways to block unwanted messages since it is costly for VZW as well operations wise to deliever these spam messages across its network. For you as a customer, as far as SPAM, you may want to make sure all the possible options for blocks regarding e-mail and web address spam is restricted via VZW's text website which is http://www.vtext.com, you can login from th ere and view those preferences.
Otherwise, VZW Customer Service now has the ability to block up to 5 numbers from calling as well as text messaging your specified number. As long as the number is not restricted or unknown and has a number associated to it, it can be blocked. You would need to contact Customer Service to have this done.