But that's what you'd be doing if you permitted user-controlled transmissions from ordinary cell phones. The analog hardware in a cell phone is tied to specific frequency bands. So you'd have user-controlled transmissions, not mediated by the cell towers, on the LTE bands.
Also, LTE-U was interfering with Wi-Fi. In general, the unlicensed bands would be a lot more useful if they weren't quite so unlicensed and every radio had to follow certain basic rules.
Actually there are rules, at least in Germany, and I assume the same is true for the US. You can use a microwave heating gun, i.e., a device that shoots a beam of microwave energy to serve similar to a leaf-blower sized hair dryer, in the ISM band(s), which might be able to saturate the LNA in 2.4 GHz radios (depending on where it is placed relative to the band-pass), but you are not allowed to use a broad-band, not-caring-about-others telecommunications radio on the same frequency. For some lower frequencies I could use them to transmit power via a resonant, one-wire transmission line to a quadrocopter to save on the weight of insulation, possibly by using aluminium-clad single mode fibers to get data capacity at the same time, so I can reduce the weight of the tether reducing overall power usage, weight and size, but if I were to use the same frequency for a direct-sequence-spread-spectrum (GPS-style) radio-location-beacon network, that would not be allowed, or only within certain restrictions usually based on both EIRP/PEP/PA-in power and techniques that allow for friendly coexistence between users of the same spectrum, i.e. with CSMA/CA or restrictions to send only 1% of the time, averaged over e.g. 24h or so.
Also, LTE-U was interfering with Wi-Fi. In general, the unlicensed bands would be a lot more useful if they weren't quite so unlicensed and every radio had to follow certain basic rules.