There will tons of guys to pick from in the offseason so why settle for him. The only argument you could make is to sign him for this year but that makes little sense either. We need to see what we already have before we pick up other people's players.
You are obviously entitled to your opinion, but what doesn't make sense to me is you saying "We need to see what we already have...," when you know what we already have. At this point none of our WRs are a mystery. All of them have played in the league for more than a few years.
You may believe it doesn't make any sense to "rent" a WR for the remainder of the season---a WR who either has or had WR1 (or what I'll call hybrid WR1-2) potential for a low round draft pick---but in top dawg's world (wink at TheRed) it makes plenty of sense. Stop trying to act like it's nonsensical. You may not agree with it, but the rationale behind the move is very sound. Likewise, I can also see why it would be considered prudent to leave it alone. It's just a matter of philosophy.
It's a unique opportunity to pick up a player who may amount to a lot at the position (which is just what the doctor ordered), or may never reach his potential due to mainly injury, but also off-field issues. If we do, it's not like we're losing something that we really shouldn't be able to get back: the talent level of a low round pick. Dealing in lower round picks is highly speculative anyway, and, to be honest, great coaches and GMs should be able to strike "gold" in UDFA, like in the case of the Pats with Kenbrell Thompkins or the Ravens with Marlon Brown, and Britt could amount to more than either one of those WRs.
On an off note, the Pats took a chance on Aqib Talib last year, now he is arguably one of the top 5 corners in the league this year. That's what good organizations do: find good players, regardless of where you get them from. Good teams don't sit on their hands and let potential talent get away (watch what Jon Baldwin becomes for the 49ers). Our WR corp needs to have game-breakers at every position, on every down (see the Broncos, Patriots, Saints and maybe even the Falcons). If Britt could add another dimension, then I'm all for it.